All-optical bistable devices

ABSTRACT

An all-optical bistable device, comprising: 
     a splitting device having first and second inputs and first and second outputs, for receiving first light beam at the first input and directing the first beam as second and third beams propagating through respective first and second outputs; first optical path between the first output and the second input and second optical path between the second output and the second input for creating combined optical path for the first and second beams at the second input; the combined optical path includes a saturable optical amplifier for enhancing and diminishing one of the second and the third beams for driving the optical amplifier into a saturation state to create one of two stable states in which one of the second and the third beams is an enhanced beam and the other beam is a diminishing beam; at least one tapping device for tapping output signal from one of the first and the second optical paths, and at least one coupling device for coupling input signal into one of the first and the second optical paths to flip between the two stable states by converting the enhanced beam into the diminishing beam.

REFERENCE TO OTHER APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/420,112, filed Oct. 21, 2002, entitled“Streaming signal control system for digital communications” and of U.S.Provisional Patent Application Ser. No. 60/440,037, filed Jan. 15, 2003,entitled “Streaming signal control system for digital communications”.

FIELD OF THE INVENTION

The invention relates to optical communications systems and opticalcomputing and more particularly to all-optical data bistable devices.

BACKGROUND AND PRIOR ART

In the field of optical communication, there is a pressing need toimprove the capacity of optical networks. Increasing the capacity of theoptical networks may be achieved by moving toward all-opticalcommunication systems. Similar demand, for higher speed exists in thecomputing field. The need for higher speed in the computing field mayalso benefit from the move towards optical computing. However, in bothfields, the communication and the computing, there are some opticaltechnologies needed but, still did not reach the level of maturity to beused. One of these desired technologies is the technology for opticalbistable devices. These devices can be used to perform logic functions,at a very high speed, in the field of optical computing and may be usedas ultra-fast activating devices to drive optical switches and gatesused in the field of all-optical communication systems for all-opticalpacket routing.

Accordingly, it is an object of the present invention to provideall-optical bistable devices;

Another object of the present invention is to provide all-opticalbistable devices including optical feedback paths;

Another object of the present invention is to provide all-opticalbistable devices including optical feedback paths having fast opticalamplifiers, such as, Solid state Optical Amplifiers (SOA) and LinearOptical Amplifiers (LOA), and

Still another object of the present invention is to provide all-opticalbistable devices having on-chip manufacturability.

SUMMARY OF THE INVENTION

The present invention provides an all-optical bistable device,comprising:

a splitting device having first and second inputs and first and secondoutputs, for receiving first light beam at the first input and directingthe first beam as second and third beams propagating through respectivefirst and second outputs;

first optical path between the first output and the second input andsecond optical path between the second output and the second input forcreating combined optical path for the first and second beams at thesecond input;

the combined optical path includes a saturable optical amplifier forenhancing and diminishing one of the second and the third beams fordriving the optical amplifier into a saturation state to create one oftwo stable states in which one of the second and the third beams is anenhanced beam and the other beam is a diminishing beam;

at least one tapping device for tapping output signal from one of thefirst and the second optical paths, and

at least one coupling device for coupling input signal into one of thefirst and the second optical paths to flip between the two stable statesby converting the enhanced beam into the diminishing beam.

In another version the present invention provides an all-opticalbistable device, comprising:

first comparator having first activating input, first threshold inputand first clamping output, the first comparator arranged to produce ahigh level clamped output signal at the first clamping output when thesignal at the first activating input is stronger than the signal at thefirst threshold input and to create a low level output signal at thefirst clamping output when the signals at the first activating and thefirst threshold inputs are similar;

second comparator having second activating input, second threshold inputand second clamping output, the second comparator arranged to produce ahigh level clamped output signal at the second clamping output when thesignal at the second activating input is stronger than the signal at thesecond threshold input and to create a low level output signal at thesecond clamping output when the signals at the second activating and thesecond threshold inputs are similar;

first optical path between the first clamping output and the secondthreshold input and second optical path between the second clampingoutput and the first threshold input for creating one of two stablestates in which one of the first and second clamping outputs producesthe high level clamped output signals and the other clamping outputproduces the low level signal;

at least one tapping device for tapping output signal from one of thefirst and the second optical paths, and

at least one coupling device for coupling input signal into one of thefirst and the second optical paths to flip between the two stable statesby converting the high level clamped output signal into the low levelsignal.

While some of the embodiments of the invention are illustrated as beingconstructed in one of the media of open space, fiber optics, radiationguides, waveguides, and planar waveguides on a chip, each of them may befabricated in any of these media. It also should be clear that while thedescriptions below describe coincidence gates they are also decodingdevices. While the optical encoded data symbols may also be described,below, as encoded signals, signals including information and controlpulses, symbols, symbol signals, spaced-pulse symbols, pulse patternsand signals, it should be clear that they all may represent opticalencoded data symbols as well as other signals defined by other termsthat may describe equivalents to optical encoded data symbols.

The invention will be described in connection with certain preferredembodiments, with reference to the following illustrative figures sothat it may be more fully understood. With reference to the figures, itis stressed that the particulars shown are by way of example and forpurposes of illustrative discussion of the preferred embodiments of thepresent invention only, and are presented in the cause of providing whatis believed to be the most useful and readily understood description ofthe principles and conceptual aspects of the invention. In this regard,no attempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to accompanying drawings, wherein:

FIGS. 1A, 1B, 1C and 1D are figurative illustrations of a gate havingtwo inputs and two outputs showing the output signals at the gateoutputs for different combinations of the input beams received at thegate inputs;

FIGS. 2A, 2B and 2C are schematic illustrations of a gate including adielectric beam-splitter device having two inputs and two outputs andshowing the output signals at the gate outputs for differentcombinations of the input beams received at the gate inputs;

FIGS. 3A, 3B and 3C are figurative illustrations of a gate including ametallic beam-splitter device having two inputs and two outputs andshowing the output signals at the gate outputs for differentcombinations of the input beams received at the gate inputs;

FIGS. 4A, 4B, 4C, 4D and 4E schematically illustrate a gate made of adual grating device having transmitting and reflecting gratingsillustrated within a prism having two inputs and two outputs and showingthe output signals at the gate outputs for different combinations of theinput beams with different relative phases received at the gate inputs;

FIGS. 5A, 5B and 5C are figurative illustrations of a gate made of aY-junction combiner device having two inputs and one output showing theoutput signal at the gate outputs for different combinations of theinput beams received at the gate inputs;

FIGS. 6A, 6B and 6C are schematic illustrations of a gate constructed bya high pitch grating device illustrated within a prism having two inputsand two outputs showing the output signals at the gate outputs fordifferent combinations of input beams received at the gate inputs;

FIGS. 7A and 7B schematically illustrate a gate made of an array ofinterleaved light guides having two inputs and one output and showingthe gate where it is fabricated by optical fibers and planar waveguides,respectively;

FIGS. 8A, 8B, 8C and 8D are figurative illustrations of a gate includinga polarizing beam splitter device and two output polarizes having twoinputs and two outputs and showing the output signals at the gateoutputs for different combinations of the input beams received at thegate inputs;

FIG. 8E is a schematic illustration of a gate produced by a directionalcoupler exhibiting behavior similar to the behavior of the gatesillustrated by FIGS. 1A–1D, 2A–2C, 3A–3C, 4A–4E, 5A–5C, 6A–6C, 7A–7B and8A–8D;

FIGS. 9A and 9B illustrate coincidence gates for symbol-selectionmechanism in a situation where the gates are in non-coincidence andcoincidence states, respectively;

FIG. 9C is a schematic illustration of a symbol copier that duplicates asingle symbol to produce input symbols for a coincidence gate;

FIG. 9D schematically illustrates a one-to-two demultiplexerrepresenting in general any one-to-many demultiplexer having outputports that each of them has a corresponding receiver that respond onlyto a specific corresponding symbol at the input;

FIG. 9E is a schematic illustration of series of symbols configured toproduce time synchronized coincidence signals;

FIGS. 9F, 9G and 9H illustrate the coincidence and non-coincidencesignals produced at the outputs of coincidence gates in response toinput signals in the from of spaced-pulses symbol, spaced-notches symbolwith non zero background, and spaced-pulses symbol including pulses withdifferent widths, respectively;

FIG. 9I illustrates the spectral distributions of wide band non-coherentand narrow band coherent signals;

FIG. 10A is a schematic illustration of the field vectors of the signalsreceived by a coincidence gate and their delayed vectorial coherentsumming produced at the outputs of the coincidence gate;

FIG. 10B illustrates exemplary presentation of vectors illustrated bytheir magnitude and phase in a complex plane;

FIG. 10C is a schematic illustration of the field vectors of the signalsand their non-zero background received by a coincidence gate and theirenhanced delayed vectorial coherent summing produced at the outputs ofthe coincidence gate;

FIG. 10D is a schematic illustration of the field vectors of the signalsreceived by a coincidence gate and their vectorial coherent summingproduced at the coincidence output of the coincidence gate that isvectorially summed in opposite phase with CW radiation to produceenhanced contrast between the coincidence signal and the backgroundsignals;

FIG. 10E schematically illustrates the embodiment for producing thevectorial summing illustrated by FIG. 10D;

FIG. 10F is a schematic illustration of the output signal produced bythe embodiment of FIG. 10E;

FIG. 11A illustrates a polarization based coincidence gate combined withcontrast enhancer device to increase the contrast between thecoincidence signal and the background;

FIG. 11B is a schematic illustration of the field vectors in variouslocations of the device of FIG. 11A shown in their corresponded timeslots;

FIGS. 11C and 11D show the intensities of the signals in variouslocations of the device of FIG. 11A;

FIG. 12A is a schematic illustration of an embodiment including acoincidence gate combined together with an optical threshold device toincrease the contrast between the coincidence and the non-coincidencepulses;

FIGS. 12B and 12C illustrate the combined transmission function of anoptical amplifier and an attenuator and the transmission function of anoptical amplifier alone, respectively;

FIGS. 12D and 12E illustrate the signals propagating in the embodimentof FIG. 12A in various locations for non-coincidence and coincidencesignals, respectively;

FIG. 12F illustrates an ideal and practical transmission function of anoptical amplifier;

FIG. 12G is a schematic illustration for a modified design of theembodiment of FIG. 12A;

FIGS. 12H and 12K illustrate the signals propagating in the embodimentof FIG. 12G in various locations for non-coincidence and coincidencesignals, respectively;

FIG. 13A is a general schematic illustration of a coincidence gatehaving two inputs and two outputs;

FIG. 13B illustrates a coincidence gate receiving input signals fromdifferent sources;

FIGS. 13C, 13D and 13E schematically illustrate specific design forclosed loop phase control, general design for closed loop phase andclock recovery control, and closed loop phase and clock recovery controlfor multiple clients, respectively;

FIG. 13F schematically illustrates a system for selecting a desired timedelay for a coincidence gate;

FIG. 13G is a schematic illustration of a system for enhancing thecontrast between the coincidence signal and the background at the outputof a coincidence gate;

FIG. 13H schematically illustrates a system including an opticalthreshold device for enhancing the contrast between the coincidencesignal and the background at the output of a coincidence gate;

FIG. 13I is a general schematic illustration of a coincidence gate thatmay or may not include any combination between a coincidence gate andany other means accompanied to the gate;

FIG. 13J illustrates a design for a time delay selector;

FIG. 14A schematically illustrates a self demultiplexer system designedto demultiplex the input information having different symbols, intodesignated outputs port according to the predetermined destinationencoded in the input symbols;

FIGS. 14B, 14C and 14D illustrate exemplary internal structures of thedividing device of the self demultiplexing system of FIG. 14A;

FIGS. 15A and 15B illustrate a device and an icon representing thisdevice, respectively, designed for converting a single pulse into asymbol signal including pair of pulses;

FIG. 15C schematically illustrates a multiplexing system forinterleaving symbols signals to form a dense stream of symbols that maybe arranged in form of Time Division Multiplexing (TDM);

FIG. 15D is a schematic illustration of a duplicating device includingcirculating loop used to increase the density (rate) of the pulses;

FIG. 15E is a schematic illustration of a demultiplexer designed forself demultiplexing of symbol signals such as the interleaved symbolsignals produced by the multiplexer of FIG. 15C;

FIGS. 15F and 15G schematically illustrate narrow pulse generators withand without threshold mechanism, respectively;

FIG. 15H is a schematic illustration of the signals produced atdifferent locations in the narrow pulse generators of FIGS. 15F and 15G;

FIG. 15J schematically illustrates a multiplexer that receives opticalpulses and interleaves them into high dense symbol signals includingpulses that are narrower than the pulses at the input of themultiplexer;

FIG. 15K schematically illustrates the foregoingmultiplexer/demultiplexer combinations as a generic schematic;

FIG. 15L schematically illustrates a contrast enhancer device used toincrease the ratio between coincidence and non coincidence pulses in themultiplexer of FIG. 15J;

FIGS. 15M and 15N are schematic illustration of the generic multiplexersand demultiplexers of FIG. 15K that may have multiple inputs and outputsand arranged in different configurations;

FIG. 15P schematically illustrates a system for self demultiplexing overmultiple layers;

FIGS. 15Q and 15R schematically illustrate self demultiplexers with andwithout data control, respectively;

FIG. 15S schematically illustrates a system for self n-by-m routingconnection;

FIG. 15T schematically illustrates a many-to-one combiner alternative tothe star combiner used in FIG. 15S;

FIGS. 16A, 16B and 16C schematically illustrates the construction ofsymbols designed for self demultiplexing/switching across multiplelayers;

FIG. 16D is a schematic illustration of self demultiplexing/switchingsystem across multiple layers;

FIG. 16E schematically illustrates a coincidence gate combined withelectronic detectors and comparator (differential amplifier) to increasethe contrast between the coincidence and the non-coincidence pulses;

FIG. 16F illustrates the intensities of the signals at the coincidenceand the non-coincidence outputs of the coincidence gate of FIG. 16E andshows the coincidence signal produced at the output of the comparator ofFIG. 16E;

FIG. 16G is a schematic illustration of the coincidence andnon-coincidence signals produced at the different layers of selfdemultiplexing/switching system;

FIG. 17 schematically illustrates a selfdemultiplexing/switching/routing Wavelength Division Multiplexing (WDM)system including multiple layers of self Code DivisionMultiplexing/demultiplexing gates;

FIG. 18A is a schematic illustrations of a selfrouting/switching/demultiplexing system made of radiation guides andincludes electronic threshold devices;

FIG. 18B schematically illustrates an exemplary threshold mechanism forthe system of FIG. 18A that includes a comparator;

FIG. 19 schematically illustrates an optical delay line fabricated on achip that includes optical couplers and mirror like edge surfaces;

FIGS. 20A and 20B schematically illustrate the configuration of FIG. 19where the mirror-like edge surfaces are replaced by Bragg reflectorgratings;

FIGS. 20C and 20D are schematic illustrations of the implementation ofthe delay line of FIG. 19 in a coincidence gate with and without a phaseshifter, respectively;

FIG. 20E schematically illustrates a delay line fabricated on a chipthat includes an open core of a loop;

FIGS. 21A, 21B, 21C and 21D schematically illustrate four versions ofmultiplexing/demultiplexing systems for symbol signals;

FIGS. 21E, 21F, 21G, and 21J schematically illustrate symbol signals,the artifact pulses that they produce and various arrangements of guardbands between the symbols;

FIG. 21K schematically illustrates narrow pulses arriving from multipleparallel channels and shows their multiplexing (interleaving) into acommon channel in a form of symbol signals;

FIG. 21L is a schematic illustration of a multiplexing system thatperforms the multiplexing illustrated by FIG. 21K;

FIG. 22A is a schematic illustration of a coincidence gate designed toreceive symbols containing more than two pulses for enhancing thecontrast between coincidence and non-coincidence signals;

FIGS. 22B and 22C illustrate the signals propagating in the embodimentof FIG. 22A in various locations;

FIG. 22D schematically illustrates a switching/routing/demultiplexingsystem that eliminates the need for time guard bands between the datasymbols and including combined coincidence gates;

FIG. 22E is a schematic illustration of an alternative design for acombined coincidence gate that may be used in the system of FIG. 22D;

FIG. 22F schematically illustrates the symbols that are demultiplexed bythe system of FIG. 22D and shows that the symbols do not include timeguard band and are closely packed;

FIGS. 23A–23F schematically illustrate the output signals at the outputsof a beam splitter for various input beams having various relativephases;

FIGS. 23G and 23H illustrate the coincidence and the non-coincidencesignals at the outputs of a coincidence gate for a data symbol signalencoded by time and phase modulation;

FIG. 23I and 23J illustrate multiplexing and demultiplexing systems fordata symbol signals modulated by time space and relative phase betweenthe pulses of the symbols;

FIGS. 23K, 23L and 23M are schematic illustrations of data symbolsignals appearing at various locations of the systems illustrated byFIGS. 231 and 23J.

FIG. 23N is a schematic illustration of a code, encoded by time spaceand phase difference between the pulses that construct the code;

FIG. 23P schematically illustrates a demultiplexing system for the codesillustrated by FIG. 23N;

FIG. 23Q illustrates the amplitudes of the output signals at outputs ofthe system of FIG. 23P when various codes of FIG. 23N are received atthe system input;

FIG. 23R is a schematic illustration of a stream of encoded pulses andtheir delayed image where the encoding done by different phases betweenthe pulses with a constant time space between them;

FIG. 23S is an illustration of a 2:1 optical data compression systemusing the input encoded signals illustrated by FIG. 23R;

FIG. 23U schematically illustrates the coincidence amplitudes generatedas a function of the phase difference between the phase shifts of theencoded signals and the phase shifts of the gates;

FIG. 23Y is an illustration of an optical data compression system usinginput encoded signals similar to the encoded signals illustrated by FIG.23R;

FIG. 24 is a schematic illustration of optical Time DivisionMultiplexing/Demultiplexing (TDM) systems;

FIG. 25A illustrates an optical packet routing system using coincidencegates;

FIG. 25B illustrates an optical demultiplexing system for packets(cells) using the packets coincidence-gates of FIG. 25A;

FIGS. 25C and 25D illustrate methods for avoiding the production ofcoincidence signals, at the header coincidence-gate, by the pulses ofthe payload;

FIG. 25E illustrates an additional design for optical packet routingsystem using coincidence gates;

FIG. 25F is a schematic illustration of the relations between an opticalpacket and its delayed image;

FIG. 25G is a schematic illustration of the relation between an opticalpacket and its corresponding broadened header coincidence-signal;

FIG. 25H is a schematic illustration of an all-photonics demultiplexingsystem for optical packets;

FIG. 25J is a schematic illustration of an all-optical demultiplexingsystem for optical packets that uses an electrical control unit;

FIG. 25K illustrates an additional design for optical packet routingsystem using coincidence gates;

FIG. 25L is a schematic illustration of the relation between an opticalpacket and its corresponding multiplied header coincidence-signal;

FIGS. 26A and 26B are schematic illustrations of an optical comparatorand its electrical equivalent, respectively;

FIG. 27A illustrates an optical bistable device using opticalcomparators similar to the comparator illustrated by FIG. 26A;

FIG. 27B is a schematic illustration of an optical bistable deviceincluding two optical feedback loops;

FIG. 27C illustrates the use of a beam splitter for input/output portsof the device of FIG. 27B;

FIG. 27D illustrates the use of a mirror for directing the beams of thedevice of FIG. 27B;

FIG. 27E illustrates the use of a directional coupler for the gate ofthe device of FIG. 27B;

FIG. 28A is an illustration of an optical bistable device using astructure of an optical mirror loop;

FIG. 28B illustrates an optical bistable device made of waveguides orplanar waveguides;

FIG. 28C illustrates a configuration in which a single beam splitter isused to couple two input signals into the device of FIG. 28D;

FIG. 28D is an illustration of an optical bistable device using retroreflectors;

FIG. 28E illustrates an optical bistable device made of waveguides orplanar waveguides;

FIG. 29A is a schematic block diagram illustration for the bistabledevices illustrated by FIGS. 27A–27E and 28A–28E;

FIGS. 29B and 29C illustrate an optical toggle device and an opticalmonostable device, respectively;

FIG. 29D is an illustration of an optical bistable device that flips itsstate according to the symbols of the header and the trailer of anoptical packet;

FIG. 30A illustrates a packet/cell gate using a header coincidence-gateand an optical monostable device;

FIG. 30B illustrates a packet/cell gate having optical header andtrailer coincidence-gates and an optical bistable device;

FIG. 30C is an illustration of an optical packet that is gated by thegate of FIG. 30B, having a header and a trailer;

FIG. 30D illustrates a packet/cell gate having optical headercoincidence-gates and an optical toggle device;

FIG. 30E is an illustration of an optical packet that is gated by thegate of FIG. 30D, having a header and a trailer encoded by time andphase modulation, and

FIGS. 30F and 30G illustrate the main coincidence pulses amplitude andphase as they are produced by the header or trailer coincidence-gate ofFIG. 30D.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 1A, 1B, 1C and 1D are figurative illustrations of a gate 100 thatdirects applied energy, for example, optical energy, based on aninteraction between two sources, such as a control source and a sourcerepresenting data. As discussed below, the gate 100 may permit theselective application of higher energy to an output port based on thetiming and configuration of inputs by interaction of the inputs andwithout the requirement for a state change of the gate 100. A discussionof various embodiments that exhibit this behavior follows the discussionof FIGS. 1A, 1B, 1C and 1D.

Referring to FIG. 1A, a gate 100 has two inputs 5 and 10 and isconfigured such that when compatible energy signals are receivedsimultaneously at the inputs 5 and 10, responsive outputs, at an outputport 15, is obtained. For example, the inputs may be optical energypulses whose phases are aligned to constructively interfere within thegate 100 or light beams whose polarization angles are in a predeterminedrelationship relative to each other and to filters within the gate 100.The gate 100 may be further configured such that if the energy receivedat the inputs has some other relationship (polarization angles, phase,or relative timing, for example) then a different output is obtained.The gate 100 may also, in embodiments, be configured to generate adifferent output signal at another output, for example output 20 wheresome of the energy is directed. For example, when a differentrelationship between the signals received at the inputs 10 and 5 exists,different signals may be output at such an additional output 20.Although only one additional output 20 is shown, more may be provided,depending on the embodiment.

In FIG. 1A, an input signal 40 includes an input symbol, representedhere by a pulse 35 applied to input 5 of the gate 100. A second input 10receives a different input symbol, represented here by the absence of acoinciding pulse (i.e., no input signal). An output signal 60, and wherepresent other output signals represented by output 63, are responsive tothe input signals. Here the output signals are represented by pulses 70and 80 generated at outputs 15 and 20, respectively. The output signalsare detected by sensors 90 and 95. Although gate 100 has two outputs 15and 20 from which signals 60 and 63 are emitted and detected by sensors90 and 95, respectively, a greater or lower number of outputs may beprovided as will be clear from the discussion of specific embodimentsbelow.

Referring now to FIG. 1B, the inputs signals change. Here, a differentinput signal 25 is represented by a pulse 30 applied to the input 10 ofthe gate 100 and no signal at input 5. A changed output signal 61 isrepresented by a pulse 71 generated at the output 15. In the illustratedcase, the output may be substantially the same whether there is a pulseat input 5 or at input 10, but not coincident. Referring to FIG. 1C,when pulses 30 and 35 are applied to both inputs 10 and 5, respectively,a different output 62 results, which includes a pulse 72, which isdifferent from either pulse 70 or 71.

By providing an appropriate detector, such as, detector 90, to the gate100, it can be determined whether a signal was applied to either input 5or 10 independently or to both in a certain temporal relationship. Thismay be determined by detecting the presence of a pulse 72 versus eitherpulse 70 or 71, for example, by comparing an intensity level of therespective pulses. Thus, for example, if a receiver is configured todetect only pulses of the form 72, a signal modulated to carry data andapplied at one of the inputs 5 or 10 may be detected as such at theoutput 15 only when a “control signal” is applied at the other input 10or 5 simultaneously and respectively. In this case, for example, a datasignal at input 5 may be considered to be passed or blocked depending onthe coincidence of a signal at input 10. Thus, one of the inputs can beregarded as a control input and the other as a data input. In FIG. 1C,signals 25 and 40 might be coherent and the relative phase between themmight be adjusted in a way that output 20 might not emit any radiation.Note that, depending on the nature of the signals applied at ports 5 and10, which output is used as the output of interest may be changed. Forexample, the phase relationship between the input signals 25 and 40 mayaffect which port 15, 20 would be better used as a more effective onefor signaling.

FIG. 1D illustrates a configuration, similar to that of FIG. 1C, exceptthat both outputs, 15 and 20, are used for signaling. The nature of thesignals applied at ports 5 and 10 may create useful signals at bothoutputs 15 and 20 that may be in a form of signals 83 and 84 carried bybeams 66 and 67, respectively. For example, the relative phase betweenbeams 25 and 40 may determine at which output port an enhanced outputdue to constructive interference appears.

Referring to FIGS. 2A, 2B and 2C, an embodiment of a device that mayexhibit behavior such as gate 100 is a dielectric beam splitter 110. Insuch an embodiment, the inputs arc optical energy. One input 115 therelative strengths of all inputs and outputs are represented by acomplex number indicating relative peak amplitude of their electricfields E-field) is a beam incident from one angle, which results in thegeneration of reflected and transmitted output ports 112 and 113 withoutput signals 145 and 150. The phase of the reflected output 150 isshown as π/2 radians ahead of that of the input 115 to indicate that arelative change of phase occurs depending on the presence and phase of asecond input 160. Each output in FIG. 2A has an intensity of about halfthat of the input beam intensity due to the effect of the beam splitter110. The intensity is proportional to the square of the E-field. In FIG.2B, the input 160 includes pulse 155 whose phase is shown arbitrarily asbeing π/2 radians behind of that of the input 115, produces a similarresult of two output signals 165 and 170 emanating from output ports 112and 113, respectively. The intensities of each of these output signalsis about half that of the input 160. Each of the inputs may includerespective pulses 125, 155 as illustrated.

It is assumed that the energy incident on the dielectric beam splitter110 consists, at least substantially, of a single wavelength of light,although, as discussed below, in further embodiments, they consist ofnon-coherent radiation such as multiple wavelengths, propagation modes,phases or any combination of them. Where the light signals arenon-coherent, the power combination effect is correspondingly differentwith simple power summing, rather than field summing, taking place.

Referring to FIG. 2C, when inputs 175 and 180 are incidentsimultaneously on the dielectric beam splitter 110, an output 197 isgenerated at output port 112 whose field corresponds to the sum of powerof the two inputs 180 and 175. The intensity of the pulse 190 of output197, being proportional to the square of the field amplitude, is thusfour times the intensity of either output 145, 150 165, 170 when onlyone input signal 115, 160 is applied alone. If an incident signal 115 or160 contains a pulse 125, 155, then the amplitude of an output pulse135, 140, 136, 141, is half that of the input pulse 125, 155 when thelatter is incident alone. If incident input signals 175 or 180 containpulses 185, 195, then the amplitude of an output pulse 190, is twicethat of either input pulse 185, 195 when the pulses 185, 195 areincident simultaneously. If the beam 197 is taken as the output, thebehavior of dielectric beam splitter 110 can be seen to fall within thedescription of the gate 100 (FIGS. 1A–1D).

Note that the output may be taken as 145, 165 or 150, 170 as well andstill fall within the description of the gate 100, depending on theinterpretation of the received signal, the relative phase between inputbeams 115 and 160, and how data is represented. When using coherentenergy, such as light, the energy ratio between the energy of thecoincidence pulse, at the coincidence output, and the energy of thenon-coincidence pulse at that output is up to four. When usingnon-coherent light this ratio is up to two. The differences between theabove ratios is due to the fact that when using coherent light thecontrol device (gate 100) acts as a field combiner while it acts as apower combiner when using non-coherent light. In addition, when usingcoherent radiation, the coincidence signal is produced at only oneoutput and the non-coincidence signal is null. Thus the energy that isdivided between two outputs, in a non-coincidence situation, is emittedfrom only one output, in a coincidence situation.

Note that if the phase of either input signal 175 or 180 is changed byis, the coincidence output pulse will emanate from the port 113 ratherthan the port 112. This effect may be used to “direct” the coincidencepulse 190 based on a phase encoding of one or both of the input signals.As will be discussed below, this along with the selective gating effectmay be used to perform a communications function as performed by aswitch or multiplexer/demultiplexer.

Referring to FIGS. 3A, 3B and 3C, a further embodiment of a device thatmay exhibit behavior such as gate 100 is a metallic beam splitter 210.In this embodiment, again, the inputs are assumed to be optical energywith the electric field represented by vectors in complex coordinates.The field magnitude is indicated by a number near the field vector. Oneinput 215 is a beam incident from one angle, which results in thegeneration of reflected and transmitted outputs 245 and 250. Some lossof energy occurs in the material of the metal film of the beam splitterso the sum of the power of the outputs 245 and 250 is about half that ofthe input 215. The phase of the reflected output 250 is shown as πradians ahead of that of the input 215, which is typical of reflectionfrom a metal. Output energy 245 is transmitted by metal beam splitter210 due to the tunneling effect and thus suffers from attenuation. Themetal attenuation can be adjusted by varying the metal thickness. Thetype of metal and its thickness are chosen to produce 50% attenuationand 50% reflectance. In FIG. 3B, the input 260 whose phase is shownarbitrarily as being π radians ahead of that of the input 215, producesa similar result of two outputs 265 and 270 whose intensities are abouta quarter that of the input 260. Outputs 265,270 adjusted to have thesame intensity and equal to quarter of the input intensity. Thisadjustment is done by choosing the reflectivity of the metal to be equalto its attenuation. Each of the inputs may include respective pulses 255and 225, as illustrated. Again, it is assumed that the energy incidenton the metallic beam splitter 210 consists, at least substantially, of asingle wavelength of light, although, as discussed below, in furtherembodiments, they consist of non-coherent radiation that may containmultiple wavelengths, propagation modes, phases, or any combination ofthem.

Referring to FIG. 3C, when inputs 275 and 280 are incidentsimultaneously on the metallic beam splitter 210, outputs 282, 297 aregenerated whose fields are equal to that of either input 280 and 275.The intensity of the outputs 282, 297 is higher by a factor of fourrelative to the outputs 265, 270, 245, 250 because no loss occurs in themetal when the phases of the incident beams 275 and 280 are in aparticular relationship and coincident on the beam splitter 210 asillustrated. The loss in the metal is reduced, incoincidence, due to afree path created by the joint and overlap between the two skin-depthson both sides of the metal, which are produced simultaneously by the twobeams that coincide. If incident signals 215 or 260 contain pulses 225,255, then the amplitude of any output pulse 235, 240, 267, 277, is aquarter that of the input pulse 225, 255 when the latter is incidentalone. If incident signals 275 or 280 contain pulses 285, 295, then theamplitude of an output pulse 290 (or 287), is equal to that of eitherinput pulse 285, 295 when the pulses 285, 295 are incidentsimultaneously. When using coherent light, the energy ratio between theenergy of the coincidence pulse, at the coincidence output, and theenergy of the non-coincidence pulse at that output is up to four as aresult of field combining. When using non-coherent light this ratio isup to two as a result of power combining and no change of the loss inthe metal of the beam splitter. If the beam 282 (or 297) is taken as theoutput, the behavior of metallic beam splitter 210 can be seen to fallwithin the description of the gate 100 (FIGS. 1A–1D).

Referring now to FIG. 4A, a dual grating device 310 has a grating 311,illustrated within a prism 299. The grating has intermittent reflective313A surfaces. Light beams 300A and 300B incident from opposite sides ofthe grating 311 generate a diffraction pattern 300C that, for example,is of one order when only one beam 300A or 300B is incident and ofanother when both beams 300A and 300B are simultaneously incident. Thisis because when beam 300B is incident alone, light passes through onlythe gaps 313D between grating elements 313C and when beam 300A isincident alone light is reflected only from the reflective surfaces313A. As a result, the effective grating pitch is of a certain order andsubstantially the same due to the identical spacing of reflectivesurfaces 313A and gaps 313D. However, when both beams 300A and 300B areincident, the effective grating pitch is doubled because the gaps 313Dare interleaved with the reflective surfaces 313A.

Referring to FIGS. 4B, 4C and 4D, yet a further embodiment of a devicethat may exhibit behavior such as gate 100 (FIG. 1) is a dual grating310. In this embodiment, again, the inputs are assumed to be opticalenergy. One input 309 is a beam incident from one angle, which resultsin the generation of reflected and transmitted outputs 307 and 305. Theresulting interference patterns 301 and 303, may have three lobes if thewavelength of the light and the grating 311 pitch are appropriatelyselected. As shown in FIG. 4C, a similar result obtains if a beam 313 isincident from another angle with transmitted and reflected interferencepatterns 319 and 321 being generated. Again, it is assumed that theenergy incident on the dual grating device 310 consists, at leastsubstantially, of a single wavelength of light, although, as discussedbelow, in further embodiments, they consist of multiple wavelengths,modes, or phases.

Referring to FIG. 4D, when inputs 309 and 313 are incidentsimultaneously on the dual grating device 310, an interference pattern329 of lower order is generated. If the pitch of the grating 311 isselected appropriately as well as the phase between beams 313 and 309,the intensity of a given part of the interference patterns 329, 327,produced when both inputs 309 and 313 are incident simultaneously, maybe four times greater than of interference patterns 301, 321, 303, 319produced when either of beams 313 or 309 is incident alone. Illustratedis the situation for zero and first order interference patterns wherethe central lobe of the interference pattern exhibits this effect. Ifincident signals 309 and 313 contain pulses then the amplitude of acorresponding output pulse has a first magnitude when the latter isincident alone. If incident signals 309 and 313 contain pulses then theamplitude of an output pulse having four times the first magnitude whenthe pulses are incident simultaneously. If light from the central lobe329A is collected and treated as an output, then the behavior of thedual grating device 310 can be seen to fall within the description ofthe gate 100 (FIGS. 1A–1D).

The intensity of the lobes in interference patterns 301, 303, 319, 321,327 and 329 are schematically illustrated and do not represent theactual relative intensity of the lobes where, actually, the side lobesare smaller than the central lobe. The transmitting gaps 313D and thereflecting elements of surface 313A can be broadened to convert grating310 into transmitting and reflecting binary grating. In such a case theside lobes has half of the intensity of the central lobe.

When using coherent light the energy ratio between the energy of thecoincidence pulse, at the coincidence output, and the energy of thenon-coincidence pulse at that output is up to four as a result of thereduction of the number of lobes due to field interference. When usingnon-coherent light the number of lobes in the interference pattern doesnot change and the above ratio is up to two as may be predicted sincethe energies are summed.

Referring now to FIG. 4E, when the relative phases of the input signalsare changed by π, the interference patterns 333 and 335 corresponding tocoinciding inputs 309A and 309B will change from a single lobe 329A totwo large lobes as indicated at 333A and 335A. The total energy outputduring coincidence and non-coincidence follows the same relationship,but the energy is divided between two lobes. With suitably locatedoptical pickups and a combiner, for picking up the total energy in thepair of lobes, e.g., 333A, and one located to pick up the energy in asingle lobe such as at 329A, this effect may be used to “direct” thecoincidence pulse 190 based on a phase encoding of one or both of theinput signals. As will be discussed below, this along with the selectivegating effect may be used to perform a communications function asperformed by a switch or multiplexer/demultiplexer.

Referring to FIGS. 5A, 5B and 5C, an optical Y-junction 346 may alsoexhibit the described properties of the gate 100 of FIGS. 1A–1D. A firstinput signal 340 may be applied to a first leg 343 with no coincidentsignal applied to the second leg 344. An output signal 345 may have anintensity magnitude of half that of the input signal 340. Similarly, asecond input signal 342 may be applied to the second leg 344 with nocoincident signal applied to the first leg 343. In that case, again, anoutput signal 348 may have an intensity magnitude of half that of theinput signal 342. Note that half of the energy is lost to the secondpropagation mode, in the coupling region 346A, and constitutes a loss,from the device at output 347. When both input signals 340 and 342 areincident simultaneously and in phase, the magnitude of an output signal350, at output 356, may be sum of the magnitudes of the input signals340 and 342. In the latter case, the energy in inputs 340 and 342 iscoupled only to the first propagation mode, in junction 346A, and allpropagates through output 347. Accordingly, when using coherentradiation, the energy of the coincidence output pulse 350 is up to fourtimes higher than the non-coincidence pulses 345, 348, depending on therelative phases of inputs 340 and 342. When using non-coherent radiationfor pulses 340, 342 the energy of the coincidence pulse 350 is only upto twice the energy of pulses 345, 348. Vector diagrams 341, 339, 352,354 and 356 are vectorial presentations of signals 340, 342, 345, 348and 350, respectively. The values accompanied to the vector diagramsindicate the field amplitudes of the vectors corresponding to thesignals that they represent.

Referring to FIGS. 6A, 6B and 6C, yet another embodiment of a devicethat may exhibit behavior such as gate 100 of FIGS. 1A–1D is a highpitch grating 360 device with a high-pitch grating 360A within atransparent prism 360B. In this embodiment, the inputs 361 and 363 are,again, optical energy. One input 361 (as in the embodiment of FIGS.2A–2C, the relative strengths of all inputs and outputs are representedby a complex number indicating relative peak amplitude of their electricor magnetic fields) is a beam incident from one angle, which results inthe generation of reflected and transmitted outputs 366 and 370 fromoutput ports 379 and 377, respectively. The phase of the reflectedoutput 366 from the port 377 is shown as π radians behind that of theinput 361 as should be for a reflection from a metal. Transmitting andreflecting metal grating 360A is a zero order grating, which means thatits transmitting openings are smaller than the radiation wavelength.Thus, the openings behave as a metallic waveguides near cutoffconditions and produce small attenuation and a phase shift of π/2radians, to transmitted output 370, relative to input 361. Each outputin FIG. 6A has an intensity of about half that of the input beamintensity 361 due to the effect of the grating 360A, and the fact thatthe intensity is proportional to the square of the E-field. In FIG. 6B,the input 363 whose phase is shown arbitrarily as being π/2 radians outof phase with input 361, produces a similar result of two outputs 374and 376 whose intensities are half that of the input 363. Each of theinputs 361 and 363 may include respective pulses 362, 372 asillustrated. Again, it is assumed that the energy incident on thegrating device 360 consists, at least substantially, of a singlewavelength of light, although, as discussed below, in furtherembodiments, they consist of multiple wavelengths or other forms ofnon-coherent radiation. While the radiation transmitted by grating 360Amay suffer attenuation, it still can have an intensity that is equal tothe intensity of radiation reflected from grating 360A. Equalizing theintensities of reflected from and transmitted through grating 360A canbe done by selecting the reflectivity, the gap size, and the thicknessof grating 360A.

Note that the port from which the coincidence pulse emerges 377 or 379can be selected based on the phase relationship of the input signals 361and 363. As in the embodiments of FIGS. 2A–2C and FIGS. 4A–4E, when thephase difference between the input signals 361 and 363 is changed by π,the port from which the coincidence pulse emanates switches. In thefurther embodiments discussed below, it should be understood that thephase-selection may be obtained by suitable change in the phase of oneor both inputs and it will not be specifically referred to in theattending discussion.

Referring to FIG. 6C, when inputs 361 and 363 are incidentsimultaneously on the grating device 360, an output 376 is generatedwhose field corresponds to the sum of power of the two inputs 361 and363. The intensity of the output 376 is thus four times the intensity ofeither output 366, 370, 376, 374 when only one input signal 361, 363 isapplied alone. If an incident signal a pulse 362, 372, then theamplitude of an output pulse 354, 368, 375, 380 is half that of theinput pulse 361 and 363 when the latter is incident alone. If inputpulses 362 and 372 are incident together, the amplitude of an outputpulse 378 is twice that of either input pulse. Thus, the grating device360 can be seen to fall within the description of the gate 100 (FIGS.1A–1D). Note that the output 374 may be taken as the output and stillfall within the description of the gate 100, depending on theinterpretation of the received signal and how data is represented. Inthe other embodiments discussed above employing gate 100 (FIGS. 1A–1D),grating 360A can be used with non-coherent light to produce acoincidence signal so that its coincidence signal intensity is up todouble the non-coincidence signal.

Referring to FIG. 7A, an alternative structure for creating the low andhigh order interference patterns exhibited by the grating of device 310of FIGS. 4A–4D uses an array of interleaved light guides 391 to projecta diffraction pattern 383 whose order depends on the coincidence of twoinputs 385 and 387. The first input 385 directs light into one set oflight guides 389A which are established at a first spacing. The secondinput 387 directs light into another set of light guides 389B which areestablished at the same spacing, but offset by one half that spacingfrom the first set and interleaved. When a light signal is applied tothe first or second input 385, 387 a higher order interference patternresults than when both receive light signals simultaneously. Thebehavior of this embodiment in conformance with the description of thegate 100 is substantially as discussed with respect to the embodiment ofFIGS. 4A–4D. Phase shifter 395 and 397 ensure that the proper phaserelationships exist at the grating output. Phase shifter 395 and 397 maybe of various types, such as, stretchers or thermal phase-shifters.

Referring now also to FIG. 7B, the light guides 389A and 389B may befabricated as laminar waveguide structures 389A and 389B usinglithographic techniques on a substrate 410 for mass production. Since,in all of the above embodiments discussed above, the maintenance of aprecise phase relationship may be essential, adjustable delay portions(phase shifter) as indicated for example at 408 may be formed on thewaveguide structures 389A and 389B which are independently controllablevia control leads 406 and 402. Various mechanisms for adjusting theindex of refraction of materials suitable for waveguide structures 389Aand 389B are known, for example, ones depending on the strength of anapplied electric field or ones depending on temperature. Thus, theadjustable delay portions 408 (typ.; Note that the nomenclature “typ.”which stands for “typical,” indicates any feature that is representativeof many similar features in a figure or in the text) may includeappropriately treated materials and electrical contacts to permit thecontrol of the phase (and more coarsely, the timing) of the signals suchthat the required interference effects are obtained. Fibers, for exampleas indicated at 412, are shown connecting the waveguides to input ports414 and 416, however, the same function of routing may be provided by athree-dimensional lithographic techniques as well. Other opticaloptically-interference generating structures may be created to providesimilar effects and the above set of embodiments is intended as beingillustrative rather than comprehensive. All of the above drawings arefigurative and features are exaggerated in scale to make the elementsand their function clearer.

Referring now to FIG. 8A, a polarizing beam splitter device 418 includesa polarization filter 423 that transmits and reflects incident opticalinputs 419A and 419B. An orientation of the polarization filter 423 isindicated by arrows 423A. As is known in the art, when an optical input419A or 419B is transmitted through the polarization filter 423, theinput field of beams 419A, 419B is reflected in proportion to the sineof the angle between the input's 419A or 419B polarization and that ofthe filter 423. That is, only the component of the input 419A or 419Bpolarization aligned with the filter's 423 polarization is transmitted,the remainder is reflected. In the figures that follow, an opticalsignal's polarization is indicated by an arrow as shown at 417illustrated in Cartesian coordinate 429A and 429B, and that of thepolarization filter 423 by arrows such as indicated at 423A.

Further polarization filters 425 and 426, with respective orientations425A and 426A, may be used to enhance the difference between coincidenceand non-coincidence outputs. That is, the outputs 428E and 428D may befurther filtered by polarization filters 425 and 426 to produce outputs424A and 424B. Two input ports I₁ and I₂ and two output ports O₁ and O₂are defined as illustrated. As discussed below, one of the two outputports O₁ and O₂ may be used alone as a selecting blocking gate or incombination so that the polarization device can be used as an outputswitch. In FIGS. 8B–8D, it is assumed that output port O₁ for purposesof discussion, but suitable orientation of the polarizations of theoptical inputs generates the same behavior at the output port O₂. Inparticular, the output port behavior is switched each time thepolarizations of both optical inputs 419A and 419B are rotated by π/2.As will become clear shortly, the present embodiment is thus similar tothe embodiments of FIGS. 2A–2C, 3A–3C, 4A–4E, 6A–6C and 7A, 7B, exceptthat polarization is used for signal attenuation/augmentation ratherthan energy or field summing.

Referring now to FIG. 8B, an optical input 419A with polarization 420Ais applied to polarization filter device 418 with the polarization ofthe optical input 419A as indicated at 420A. The orientation of thepolarization filter 423 is the same as that of the optical input 419A.Therefore, substantially all of the energy of the optical input 419A istransmitted as output 428A, with the polarization orientation, indicatedat 421A, being the same as the optical input 420A. As indicated by theboldface numerals, the field amplitude of the optical input 419A andoutput 428A are both substantially the same and equal to 1 in arbitraryunits.

The output 428A, according to a further embodiment, may be filtered bypolarization filter 425 with the polarization orientation indicated. Thelatter, as shown, forms an approximately π/4 angle with the orientationof the polarization filter 425 so that the output signal 428A isattenuated accordingly, causing the magnitude of the output E-field 424Ato be √{square root over (2)}/2 and its orientation to be aligned withthat of the filter 425 as indicated at 422A.

Referring now to FIG. 8C, an optical input 419B with polarization 420Bis applied to polarization filter device 418 with the polarization ofthe optical input 419B as indicated at 420B. The orientation of thepolarization filter 423 is perpendicular to that of the optical input419B. Therefore, substantially all of the energy of the optical input419B is reflected as output 428B, with the polarization orientation,indicated at 421B, being the same as the optical input 420B. Asindicated by the boldface numerals, the field amplitude of the opticalinput 419B and output 428B are both substantially the same and equal to1 in arbitrary units.

As in the embodiments of FIG. 8B, the output 428B, according to afurther embodiment, may be filtered by polarization filter 425 with thepolarization orientation indicated. The latter, as shown, forms anapproximately π/4 angle with the orientation of the polarization filter425 so that the output signal 428B is attenuated accordingly, causingthe magnitude of the output E-field 424B to be √{square root over (2)}/2and its orientation to be aligned with that of the filter 425 asindicated at 422B.

Referring now to FIG. 8D, optical inputs 419A and 419B withpolarizations 420A and 420B, respectively, are applied to polarizationfilter device 418 simultaneously. The polarizations of the opticalinputs 419A and 419B are as indicated at 420A and 420B. The orientationof the polarization filter 423 is the same as that of the optical input419A and perpendicular to that of optical input 419B. Therefore, thetransmitted field of optical input 419A is combined with the reflectedoptical input 419B in the manner of the beam splitter embodiments and acombined output 428C obtained, with the polarization orientation,indicated at 421C, being the vector sum of those of the tow inputs 419Aand 419B. The power of the output 428C is the sum of the powers of theoptical inputs 420A and 420B. Therefore, its field amplitude is equal to√{square root over (2)}, as indicated by the boldface numerals showingarbitrary units.

As in the embodiments of FIGS. 8B and 8C, the output 428C in FIG. 8D,according to a further embodiment, may be filtered by polarizationfilter 425 with the polarization orientation indicated. The latter, asshown, forms an approximately zero angle with the orientation of thepolarization filter 425 so that the output signal 428C is notattenuated. Thus, the magnitude of the output E-field 424C is √{squareroot over (2)} and its orientation is aligned with that of the filter425 as indicated at 422C.

As should be clear from the above discussion, an output 424C isobtained, when inputs 419A and 419B are coincident, whose intensitymagnitude is four times that of the output 424A or 424B when eitherinput 419A or 419B is incident by itself. This behavior is similar toembodiments previously discussed. If light having multiple frequenciesor phases (or multimode light) is used, the polarization device 418 actsas a simple power summer rather than a field summer. Thus, the power ofthe output will not be as great as when coherent light, suitablephase-aligned, is used. As should also be clear from the properties ofthe polarization filter device 418, if the polarization angles of theinputs 419A and 419B are rotated by π/2 (in either direction), similarresults will be obtained as above, except that instead of the outputs428A, 428B and 428C being generated at output O₁, they will be generatedat O₂, such as illustrated by output 428D of FIG. 8A.

Using the configuration of FIG. 8D when polarization filter 425 isremoved, resulting in a signal 424C, at the coincidence output, that itsintensity, when beams 419A and 419B are applied simultaneously, is onlytwice the intensity when only one input of inputs 419A or 419B isapplied.

FIG. 8E illustrates a directional coupler device 443. Device 443 isconstructed from a directional coupler 438 that has two input ports I₁and I₂ indicated at 434A and 434C, respectively, and two output ports O₁and O₂ indicated at 434B and 434D, respectively. Waveguide portions 432(typ.) interconnect the directional coupler 438 with the ports 434Athrough 434D as illustrated. The directional coupler device 443 may beformed on a substrate 441 using lithographic techniques or manufacturedin any suitable manner as a discrete component or one of many on asingle optical chip, as desired.

The directional coupler device 443 may also be used as a gate deviceconforming to the description for gate 100, as discussed with referenceto Table 1, below.

TABLE 1 Field magnitudes of inputs and outputs for directionalcoupler-based gate I₁ I₂ O₁ O₂ Q₁ Power Field   {square root over (2)} 01   j 1 Magnitude/ 0 −{square root over (2)}j 1 −j 1 phase   {squareroot over (2)} −{square root over (2)}j 2 0 4 0   {square root over (2)}  j 1 1 −{square root over (2)}j 0 −j 1 1 −{square root over (2)}j  {square root over (2)} 0 2 0

When the indicated inputs I₁ and I₂ are applied in combination in agiven row, the corresponding outputs O₁ and O₂ are given in the same rowresult. The phase relationships are relative and depend on the precisestructure and materials of the directional coupler device 443, whichdetermine delays, coupling length, etc. As will be clear to those ofskill in the relevant fields, a structure may be created to provide theabove behavior or a simile. As should be immediately clear, the ratio ofpower at output port O₁ when the input signals are coincident is fourtimes that when one signal arrives at a time, as indicated in Table 1.Also, if the phases of the inputs are rotated by π/2, as indicated inthe last three rows, the large coincidence output is generated at portO₂ instead of port O₁. When non-coherent radiation is used, both outputsO₁ and O₂ produce output signals, even when both inputs appliedsimultaneously, resulting in a coincidence output signal that itsintensity is only up to twice the intensity when only one input isapplied alone.

In general it should be understood that for all the embodimentsdescribed above (2A–2C, 3A–3C, 5A–5C, 4A–4E, 6A–6C, 7A–7B and 8A–8E) inaccordance to FIGS. 1A–1D, and when using coherent radiation, thecoincidence output, when the two inputs are applied simultaneously, mayproduce a signal that its intensity is within a range between 0 up tofour times the intensity when either input is applied alone. Thecoincidence output signal may be adjusted, to be at any intensity valuewithin the above described range, by the relative phase and polarizationbetween the two input beams. For non coherent radiation the intensity ofthe coincidence output, when the two input beams are applied together,may be higher up to twice the intensity, at this output, when eitherinput beam is applied alone.

Accordingly, it can be seen that the above described summing gates,which are all represented by gate 100 of FIGS. 1A–1D, produce low andhigh level amplitude signals, at their coincidence output, correspondingto non-coincidence and coincidence states, respectively.

Thus the input state (coincidence or non-coincidence state) of gates 100can be detected at their outputs by monitoring their output signal usingdetectors such as detectors 90 and 95 of FIGS. 1A–1D.

Alternatively, the input state of gates 100 can be detected at theiroutputs using threshold devices. The lower and the higher level signalsat the outputs of gates 100, corresponding to non-coincidence andcoincidence states at the inputs of gate 100, can be adjusted to bebelow and above the threshold level of a threshold device into whichthese signals are fed in order to detect the input states.

The use of a threshold device that follows the summing gate produces anAND logic gate that its output is in logic states “1” or zero when itsinputs are in coincidence or non-coincidence states, respectively. TheAND gate includes two major units, a summing gate (such as the summinggates 100 described above) and a threshold device (such as describedbelow). The combination of summing gates with threshold devices toproduce AND gates, is described, in details, below.

Referring now to FIGS. 9A and 9B, a symbol-selection mechanism can causethe output of a first signal level pulse when a particular spaced-pulsesymbol (to be described presently) is applied to a matching gate and asecond signal level pulse when the symbols is applied to a non-matchinggate. To illustrate this, refer to the identical signals 450 and 452applied to a gate 100 through inputs 458 and 456, respectively. Eachsignal 450 and 452 containing a pair of pulses 450A and 450B and 452Aand 452B, respectively. The time spacing between the signal pulses 450Aand 450B is equal to Δt₂. The same time spacing Δt₂ also separatessignal pulses 452A and 452B. One signal 450 passes through a time delay468 and the other does not. If the temporal spacing between the pulsesmatches the delay, two pulses will be coincident on the inputs 456 and458 producing a coincidence output at port 460.

In FIG. 9A, the situation where the spacing between pulses 450A and 450B(which is identical to the spacing between pulses 452A and 452B) doesnot match the delay of the time delay 468. The latter may be simply adelay line (delay guide). At output 460, the alignment of the signals450 and 452 is illustrated by pairs of pulses 461A and 461B and 462A and462B, respectively, showing that neither of the pulses 461A, 461B, 462Aor 462B is aligned with another pulse, in this group of pulses, due tothe difference between the time space between the pulses of signals 450and 452 and the delay time Δt₁ of delayer 468. The output generated issimply the sum of the non-coincidence outputs of the respective inputsignals 450 and 452 which is shown at output 460 as a string pulses 466of relatively low amplitude compared to the situation in FIG. 9B,discussed next.

In FIG. 9B, the situation where the spacing between pulses 450A and 450B(which is identical to the spacing between pulses 452A and 452B) matchesthe delay Δt₂ of the time delayer 469. At output 460 the alignment ofthe signals 450 and 452 is illustrated by pairs of pulses 464A and 464B,and 463A and 463B, respectively showing that two of the pulses 463A and464B are aligned due to the matching between the time space between thepulses of signals 450 and 452 and the delay time Δt₂ of delayer 469. Asa result, a sequence of pulses such as shown at 470A, 472 and 470B isoutput at the output port 460, with the pulse 472 being a result of thecoincidence of pulses 452A and 450B (corresponding to the coincidencebetween pulses 463A and 464B) as illustrated at output 460. Thiscoincidence situation corresponds to the situation illustrated in FIG.1C in that pulse 472 may be substantially greater due to theaugmentation due to the summing performed by gate 100. Pulse 472 may bedetected in a suitable receiver configured to, for example, registerpulses of an amplitude of the coincidence pulse 472 and screen cut anysmaller pulses, such as non-coincidence pulses 470A, 470B and 466 ofFIG. 9A.

FIGS. 9A and 9B illustrate situations in which the input signals 450 and452 may be generated by independent sources or carried on independentmedia (fibers, channels) from different locations.

Referring now also to FIG. 9C, the separate signals 450 and 452 of FIGS.9A and 9B could be derived from a single signal 430 by means of splitter437, such as an optical Y-junction or directional coupler. Splitter 437generates two outputs 431A and 431B, each an image of the applied signal430 and containing up to half the power of the applied signal 430.Instead of a Y-junction or directional coupler, a beam splitter or othersuitable device may be used. Signals 431A and 431B may be applied, assignals 450 and 452, to delayer 468 (469 in case of FIG. 9B) and input456 of gate 100 of FIGS. 9A and 9B, respectively. Thus, a time delay Δt₁or Δt₂ for delayers 469 or 468, respectively, delays one signal 450,which is applied to one of the input ports 458 of gate 100. Thenon-delayed signal 452 is applied at the other input port 456. If thetiming of the signals is such that none of the pulses 450A, 450Bcoincides with a pulse 452A, 452B in gate 100, a sequence of pulses,such as shown at sequence of pulses 466 of FIG. 9A is output at theoutput port 460. If, however, the magnitude of a time delay 469 matchesthe pulse spacing Δt₂ one pulse of pulses 450A, 450B will coincide witha pulse of pulses 452A, 452B coincide in gate 100 causing a coincidencepulse 472 of FIG. 9B to be generated.

Further below it will describe in more detail how a variety ofcommunications systems may be configured around the effect describedwith respect to FIGS. 9A and 9B. For the moment, it may be helpful toreview a basic switch mechanism with reference to FIGS. 9A, 9B, 9C and9D. First, it may be observed how the above coincidence effect mayenable the high-speed demultiplexing of a signal 450. The signal 450,containing pulses 450A and 450B separated by a time difference Δt₂ isapplied to a splitter 453A, sending images of signal 450, to a secondlayer of splitters that includes splitters 453B and 453C. Thus, imagesof the signal 450 are applied to all the input ports (See ports 456 and458 in FIGS. 9A and 9B) of two identical gates 455A and 455B of the typeindicated as gate 100 and described with reference to FIG. 9A.

By applying the signal 450, via splitters 453A, 453B and 453C to twogates 455A and 455B, each with a different delay device 468 and 469,pulses of magnitude 472 (“coincidence pulses”) will be output in outputsignals 460A or 460B only if the corresponding time delay Δt₁ or Δt₂ ofrespective time delay device 468 or 469 of gate 455A or 455B matches thedelay between the pulses 450A and 450B. Thus, coincidence pulses willonly be transmitted to the receiver 465A and 465B whose correspondingtime delay device 468 and 469 matches the delay between the pulses 450Aand 450B. If receivers 465A and 465B are configured to be unresponsiveto signal levels of magnitude below a predefined threshold that is abovethat of non-coincidence pulses 466 of FIG. 9A and below that ofcoincidence pulse 472 of FIG. 9B, only pulse-pairs spaced apart by adelay that matches the time delay of a corresponding time delay device468 or 469 will produce a signal at corresponding receiver 465A, 465B.The number of receivers that could be distinguished is equal to anynumber of allowed pulse spacing according to this symbols scheme.

Any number of gates 100 may be added in parallel to the configuration ofFIG. 9D as will be shown in more detailed examples below. Pulse-pairswith different time spacing between their pulses may be added to thesignal 450. Each pulse pair may correspond to a different coincidencegate having time delay device added to time delay devices 468 and 469,each delay device being connected as illustrated to a respective gate100. Each gate 100 output may have a respective receiver such asreceivers 465A and 465B. In that case, the receivers will only receivecoincidence pulses if the pulse spacing Or d pulse pair matches the timedelay of delay device of a corresponding gate 100. Thus, such a systemacts as a demultiplexer, a two port demultipler being the configurationof FIG. 9D, but expandable to arbitrary number of outputs.

Referring now to FIG. 9E, for some configurations, when using the pulsespacing symbology, it may be preferred for the coincidence pulses of aseries of symbols to occur at regular intervals. For example this may beuseful for synchronization recovery in a system that receives signalsfrom multiple transmitters each coming from different switches withdifferent gate arrays (note the discussion of multiplexers anddemultiplexers below). To ensure the coincidence pulses occur at regularintervals irrespective of the spacing, one of the pulses of every pairforming a symbol may always be placed at the last time slot and thepulse in front of it used to control the spacing. For example, pulse124A pairs with pulse 124B to form a symbol. The allowed time paces(including times slots t₁ to t₆) are shown at 123 (typ.). Pulse 124C and124D form another pair defining another symbol. Pulses 124E and 124Fform yet another pair. In all cases, the trailing symbol 124A, 124D and124E are in time slot t₁. This means that even though the delay mayvary, the coincidence pulses occur at regular intervals (at time slotst₁). The figure assumes the pulses pass through a gate from left toright. It should be clear that any symbol including pair of spacedpulses may cause the coincidence gate to produce only one coincidencesignal. Accordingly, each symbol includes one data pulse and one controlpulse. Defining the control pulse and the data pulse within the pulsepair is arbitrary and may be arranged in any configuration. For example,the data pulse may be the first pulse and the control pulse may thesecond delayed pulse or vice versa.

Referring to FIGS. 9F and 9G, there are various ways of forming thesymbols that may allow symbol selection as discussed above. For example,FIG. 9F shows input symbol 473, corresponding to input signal 450 ofFIGS. 9A and 9B, blocked data symbol 475, corresponding to coincidencepulse 472 formed at the output of the coincidence gate of FIG. 9B, andpassed data symbol 476, corresponding to signal 466 produced at theoutput of the coincidence gate of FIG. 9A, all produced by thespaced-pulse modulation scheme discussed above. The zero-level isindicated at 479. But the mirror image of this format, as shown in FIG.9G, would work equally-well. That is, notches 474 in an otherwiseelevated signal level (e.g., voltage, current, intensity, etc.) ratherthan pulses, may be spaced apart by selected a spacing to create azero-level 477 (or a level below some maximum threshold) signal that isregistered by a receiver as representing data directed to it. Non-zeronotches would be treated as artifact. Again, the zero-level is indicatedat 479.

FIG. 9H illustrates another scheme for controlling the output from acoincidence gate to provide for coincidence between a single broad pulse473A and a series of pulses 473B representing multiple data bits. It maybe confirmed by inspection that with appropriate time delay, the broadpulse 473A may be made to coincide with all of the series of pulses 473Bto form a series of coincidence pulses 473C. Here the allowed time slotswould have to be broad enough ensure that when passed through a gatewith a time delay different from that for which the symbol (473A and473B) was formed (not shown), the non-coincidence output indicated at473D is formed.

Referring to FIG. 9I, note that while in the foregoing embodiments, ithas been assumed that each embodiment of a gate (e.g., 100) caused aninterference effect that required the use of a narrow band offrequencies and a proper phase match, this is not essential. Thebehavior described with respect to the gate 100 with reference to FIGS.1A-1D may be obtained by using light having a range of wavelengths witha non-coherent summing process providing the behavior described withreference to FIGS. 1A–1D. That is, the identical components may be used(although the relative cost/value equation of them may be shiftedsomewhat) to achieve up to a 2:1 ratio between coincident andnon-coincident signals rather than up to a 4:1 (or up to a 9:1 ratio inembodiments discussed further below) as where coherent summing is used.FIG. 9I is a figurative illustration of a signal 480 that has its powerdistributed over a relatively wide range of frequencies (e.g., wavepacket) and a narrow-band signal 481 one in which the range is verynarrow (e.g., “single” wavelength channel of a wavelength divisionmultiplexing (WDM) optical system). Signals 480 and 481 may be producedby Light Emitting Diode (LED) and Distributed Bragg Reflector (DBR)laser, respectively.

Referring now to FIG. 10A, coherent summing of narrow-band (narrowspectrum) signals preferably takes account of the relative phases ofsignals being added. In FIG. 10A, one signal with a spaced-pulse symbolhaving pulses 483A and 483B is represented by 483 and a time-delayedcopy (with a phase shift of −π/2 radians) of the same signal by 485. Thetime delay between signal 483 and 485 is equal to the time space betweenpulses 483A and 483B. The coherent sum of signals 483 and 485 producedby gate 100, such as gate 110 illustrated in FIGS. 2A to 2C, isrepresented by 495 (495A and 495B). Each signal 483, 485, 495 isrepresented by a series of icons 490 positioned in their correspondingtime slots t₁–t₁₀ (illustrated in a complex plane), for example the oneindicated at 489, which indicates the magnitude and phase of the fieldat a particular time instant (either electric or magnetic). FIG. 10B,illustrates the presentation of the field vectors. Each icon 489C–489Fhas a vector such as indicated at 489B, in a complex plane indicated byaxes such as at 489A. Thus, vector 489B represents the magnitude andphase of the field, which may arbitrarily be designated as the electricfield, but it does not matter since it is the relative phases of summedsignals that are of concern. The first icon 489C indicates the signalhas a phase of j (with j=√{square root over (−1)} representing theimaginary axis) and a certain magnitude, which may be assumed here to beunity for convenience. The second, third, and fourth (489D, 489E and489F) indicate a signal of identical magnitude as 489C, but havingphases of 1, −j, and −1, respectively (a numeral alone might be addedfor indicating only the magnitude with no reference to the phase).

Referring again to FIG. 10A, when signals 483 and 485 are summedcoherently, the result is the signal 495 which has two pulses 491A and491B whose field magnitudes are equal to 1/√{square root over (2)} andsignal 493 whose field magnitude is equal to twice that magnitude. Thus,the signal that is output is equal as shown at 497. The summing processrepresented is assumed to be modeled on the dielectric beam splitter ofFIGS. 2A–2C where the reflected beam is rotated by π/2 radians (Phaseshift) and the transmitted beam is not rotated (no phase shift). Thus,the total energy in the coincidence pulse 497C is equal to the totalenergy in the applied pulses 483A and 485B (485B is the delayed copy ofpulse 483B and is not shown) and that in the non-coincidence pulses 497Aand 497B is half the energy in one of the applied pulses 483A and 483Bwith the phases of the output as shown. Thus, the total energy of thecoincidence pulse 497C is four times that of the non-coincidence pulses497A and 497B.

Referring again to FIG. 10C, a signal 501 has a non-zero base level suchthat the field amplitude of the pulse is three times higher than that ofthe background level and with opposite phase. Arbitrarily choosing thephase of the pulse in signal 501 to be zero, results in a backgroundhaving a phase of π. The relative intensity of a resulting coincidencepulse 511 is nine times the intensity of the signal anywhere else. Inthis case, the non-coincidence pulses in the signal, at the coincidenceoutput, have the same intensity as the constant flat background. Forexample, the input signal 501, which may be applied as signal 115 (inFIGS. 2A–2C), has a pair of pulses, such as indicated at 499 and 499A(499 typ.), at time slots t₃ and t₅, respectively. The field magnitudeof pulses 499 (typ.) is arbitrarily chosen as unity. Elsewhere, (e.g.,time slot t₁, t₂, t₄, and t₆–t₁₀, (which may be identified as abackground level) the input signal 501 has a field magnitude ofone-third and with a phase difference of π radians relative to thepulses 499 (typ.).

Input signal 503 also does not have a zero level. The field amplitude ofthe pulse is in opposite phase relative to the field amplitude of thebackground level and is three times higher. Input signal 503, which maybe applied as signal 160 (in FIGS. 2A–2C), is a time and phase shiftedversion of signal 501, which may provided by choice of a suitable delayas discussed with reference to FIG. 9B and elsewhere. The phasedifference between the signal 501 and 503 is −π/2 radians, which meansthat the pulse of signal 503 has a phase −j and the background of thatsignal is in a phase of +j, as illustrated by the clockwise rotation ofthe vectors 489E (FIG. 10B).

Note that there are only four distinct field sums that arise in theabove context;

-   -   1. The background of signal 501 is added to the background of        503 as in time slot 1.    -   2. The pulse of signal 501 is added to the background of signal        503 as in time slot 3.    -   3. The pulse of signal 501 is added to a pulse of signal 503 as        in time slot 5.    -   4. The background of signal 501 is added to the pulse of signal        503 as in time slot 7.        In general all the situations result by vectorialy adding the        signals in the corresponding time slots in the manner of the        dielectric beam splitter of FIGS. 2A–2C (i.e., summing the        fields of signals 501 and 503 after dividing them by √{square        root over (2)} and rotating the phase of signal 503, reflected        by the beam splitter, by π/2 radians).

In situation 1, at time slot t₁, for example, where two backgroundlevels line up, the resulting magnitude and phase of the signal outputat 197 of FIG. 2C, is obtained by adding the field magnitudes aftermultiplying the background field of signal 503 by j (equivalent to aphase rotation of π/2 radians) and dividing the result by √{square rootover (2)} to get:

$\frac{\left( {{- \frac{1}{3}} + {j*\frac{j}{3}}} \right)}{\sqrt{2}} = {- \frac{\sqrt{2}}{3}}$and the energy is 2/9.

In situation 2, at time slot t₃, adding the pulse 499 in slot t₃ to thetime and phase shifted background level signal 503 in the same way givesa field magnitude of:

$\frac{\left( {1 + {j*\frac{j}{3}}} \right)}{\sqrt{2}} = \frac{\sqrt{2}}{3}$and the corresponding energy is 2/9.

In situation 3, at time slot t₅, a pulse 511 is generated with amagnitude that is:

$\frac{\left( {1 - {j*j}} \right)}{\sqrt{2}} = \sqrt{2}$and the corresponding energy of the coincidence signal at thecoincidence output is 2.

In situation 4, at time slot t₇, the field amplitude is derived in asimilar way to given:

$\frac{\left( {{- \frac{1}{3}} - {j*j}} \right)}{\sqrt{2}} = \frac{\sqrt{2}}{3}$and the corresponded energy is 2/9.

It can be seen that only situation 3 produces a coincidence signal withintensity of 2. All the other situations are related to the backgroundlevel and are with equal intensity of 2/9. This means that thebackground is flat and that the energy of the coincidence pulse is ninetimes the intensity level of the background.

The output 507B from the non-coincidence output has a zero magnitude atall points except in time slots t₃ and t₇, where the intensity magnitudeof pulse portions 513A and 509A, respectively, is 8/9 and the pulsefield magnitudes are

${{{2 \cdot \frac{\sqrt{2}}{3}}j\mspace{14mu}{and}}\mspace{14mu} - {{2 \cdot \frac{\sqrt{2}}{3}}j}},$respectively. Note that if the time shift of signal 503 is not such thatany pulses line up, the resulting signal from the coincidence output andthe non-coincidence output will have a flat intensity magnitude of 2/9and serial of four pulses with intensity magnitude of 8/9, respectively.It can be seen that in any situation the sum of the energies at theoutputs is equal to the sum of the energies in the inputs.

The advantage of a 9:1 ratio in magnitude between pulse signal 511corresponding to pulse portion 509 at output 507A (at time slot t₃) andbackground level 512, constructed by artifact pulses, such as, signalportion 513 in time slot t₃ of output 507A should be clear from theforegoing where a gate exhibiting these properties is used as amechanism for switching such as discussed with reference to FIG. 9D andelsewhere. In particular, in such a system, less precision and accuracyare required in a receiver to distinguish a transmitted coincidence datapulse 511 from the background or from a symbol 430 (FIG. 9C) that is nottransmitted because of a failure of gate 100 to provide the perfectconditions, such as, phase and time matching needed to produce thehighest coincidence signal.

Referring now to FIGS. 10D and 10E, the contrast in a signal 529 from acoincidence output of a coincidence gate (e.g., any embodiments of gate100) having a coincidence pulse 529A flanked by vestigial pulses 529Band 529C may be enhanced by an amplification process. The signal 529 hasan intensity ratio between coincidence pulse 529A and artifact orbackground level 529D (artifact including any vestigial pulses 529B and529C) of 4:1. A device for providing the enhancement process isillustrated in FIG. 10E. Here, a continuous wavelength (CW) laser source515, whose amplitude is adjusted to half the field amplitude of thevestigial pulses 529B and 529C is added to them, with a phase angledifference of π radians, by means of a summer 517. To accomplish this, asignal from an output 461 of a gate 449 (which gate 449 may be asdescribed with reference to gate 100, earlier) receives a signal at afirst input 457 having pulses (e.g., signal 523 of FIG. 10D havingpulses 535 (typ.)) and a time-delayed version thereof, via time delay469, at port 457A. A coincidence signal, 529A (FIG. 10D), is generatedat coincidence output port 461. The summer 517 may include a reverseY-junction waveguide, a directional coupler, a beam-splitter, or anysuitable device, adjusting the phase of the signal being injected, bylaser 515, to ensure the summation is as illustrated in FIG. 10D anddiscussed presently.

Referring specifically to FIGS. 10D, 10E and 10F the input signal 523has a pair of pulses 535 (typ.) which may be added to a time andphase-rotate version of itself 527, as discussed above, to generate anoutput signal 529 on a coincidence output 461. The latter signal 537added by means of the CW laser source 515 and summer 517 results in thesignal 533 being output at 519. As may be confirmed by inspection, theresulting signal has a pulse 543 whose intensity is nine times theintensity level of the flanking artifact 541 and that of the background539 signal.

The field amplitudes of the coincidence pulse and the non-coincidencepulses are 2 and 1, respectively. The signal has a zero backgroundlevel. After subtracting the CW field that has magnitude of ½, thefields magnitudes of the coincidence pulse, the non-coincidence pulses,and the background level are 1.5, 0.5 and −0.5, with their correspondingintensities of 2.25, 0.25 and 0.25, respectively.

It can be seen that all the possible situations, excluding coincidence,are characterized by a power level of 0.25, which creates a flatbackground level. The coincidence pulse has an energy of 2.25 which isnine times higher than the energy of the background level.

Note that although in the embodiments discussed above the signals addedwere derived from a common source, it is clear that they may begenerated from independent sources. For example, a data signal appliedat one port of a gate such as gate 100 could be switched by alocally-generated control signal applied at the other port. In such acase, it may be necessary to provide timing and phase recovery (PhaseLock Loop (PLL)), topics that are discussed in more detail below toprovide the above result. FIG. 10F shows the intensity of the outputsignal 521.

Referring now to FIG. 11A, a gate 459 receives signal input 551B at gateinput 457 and signal input 551C at gate input 457A delayed by Δt₂ afterdelayer 469, which should be understood as being from a single source asdiscussed relative to FIG. 9C, or from separate signal and controlsources. Gate 459 is assumed to exhibit the behavior of the polarizationbeam splitter of FIGS. 8A–8D, for purposes of illustration, but may bemade in accord with many of the other embodiments discussed herein. Acoincidence output port 461 applies an output signal 551D to apolarization filter. When coherent summing takes place within gate 459,the transverse polarization of the signals results in a vectorialaddition of the fields such that output signal 551D obeys the cosine lawin dependence on the polarization orientation of the signals at inputs551B and 551C. Output signal 551D is then filtered by polarizationfilter 566 to produce final output 519.

The functionality of the embodiment of FIG. 11A is similar to that ofFIGS. 8A–8D, as can be confirmed by reference to FIG. 11B which showsthe polarization angles and field magnitude rather than the phase andfield magnitude in a set of time slots t₁–t₁₀, but is otherwise similarto FIGS. 10A, 10C and 10D. Here, signals 551C and 5511B correspond tothe signals 554 and 556. These are added coherently to produce signal558. The effect of filtering by the polarization filter 566 isillustrated at 568 and in FIG. 11C. In signal 568, as may be confirmedby inspection, the ratio of the power magnitude of the coincidence pulse569 (in time slot t₅) is four times that of the artifact (571 and intime slots t₃ and t₇).

As discussed with respect to signal 533 of the embodiment of FIG. 10D,and illustrated by signal 521 in FIG. 10F, the ratio of coincidencepulse 573 to artifact 575 of FIG. 11D, can be raised in signal 568 ofFIG. 11B to up to 9:1. This is achieved by adding a constant levelsignal 578 (similar to signal 531 of FIG. 10D) received from terminal551E to be combined coherently with opposite phase to signal 551D, bycombiner 552, to obtain the enhanced signal 567. Also, as in thesituation of FIG. 10C, the constant level signal 578 can be distributedto the original signals 554 and 556 of FIG. 11B such that the 9:1 ratiois obtained at output signal 551D at the point of coherent summing inthe gate 459, so that a separate step is avoided.

Referring now to FIG. 12A, another refinement of the gate 100 is to usean effect, such as amplification (or limiting) processes, to reducebackground and artifact in a signal to zero so that transmitted pulses(such as 521 at FIG. 10F) have, in principle, up to an infinite ratio ofintensity to that of artifact or background level. This may be done by acancellation device (optical threshold device) illustrated at 690.Signal 613 from gate 614 (such as a gate 100 with a time delay andsplitter as discussed above) is split into two parallel signal paths 627and 623 by a splitter 619. An optical Non Linear Element (NLE), such asoptical amplifier 615, amplifies signals on one of the signal paths 627and adjusts the resulting signal on an output path 625 by means of asignal attenuator 617. The delay of signal path 627, 615, 625, 617 and629 is assumed equal to the delay of signal path 623 with a π/2 phasedifference whose significance will be explained below. A summer 621 addsthe signals on signal paths 629 and 623 to provide a conditioned signaloutput at 613A.

Referring now to FIG. 12B, the amplifier 615 and attenuator 617 of FIG.12A, in combination, are characterized by a gain curve 615D exhibitingsaturation when the magnitude of the signal on its input (path 627) goesbeyond a certain level. Ideally, the gain curve is as indicated at 615D.This can be achieved approximately because of the behavior of certainoptical amplifiers, such as Erbium Doped Amplifier Fiber (EDAF),Solid-state Optical Amplifier (SOA), Linear Optical Amplifier (LOA) andRaman Amplifier, which has a gain curve 615C as illustrated in FIG. 12C.The gain curve 615C has two main regions, one 560B in which the gain issubstantially constant with high-valued and another 560A, identified asa saturation region, whose slope is substantially constant, but muchshallower. The gain curve of FIG. 12B, reduces the slopes of both gaincurves by means of the attenuator 617 so that the region 560A is maderelatively horizontally flat as is the region 615A, while the gain inregion 560B is still effective to amplify as in the region 615B.

FIGS. 12D and 12E illustrate the effect of the configuration of FIG. 12Aat each stage when signal 613 has only artifact pulses, as illustratedat 641, and when the signal contains a coincidence pulse, as illustratedat 647. The signals of FIGS. 12D and 12E are illustrated by a schemewhere a signal with a π radians phase shift is drawn upside down. In thefirst case, the signal 641, which has only artifact and background, isplaced on signal paths 623 and 627. The signal 633 on path 627 isamplified by the optical amplifier. The optical amplifier saturationlevel is such that artifact is amplified linearly and any level abovethe highest anticipated artifact results in saturation. The saturationpoint can be higher, however, as will be clear from the followingdescription. As a result of the gain curve characterized above, when asignal 641 containing only artifact passes through the configuration ofFIG. 12A, the incoming signal 641 is divided into duplicate copies 631and 633 (except for energy loss in the splitting)

Signal 633, propagating through path 627 is amplified, by amplifier 615in the linear region to produce a higher-level signal 635 withadditional phase shift of π/2 radians. Signal 635 is then attenuated, byattenuator 617 to produce signal 637. The phase of signal 637 iscoherently shifted by π/2 radians out of phase with respect to signal631, at the input of combiner 621. Signal 637 is then added, withopposite relative phases, to signal 631, by combiner 621, resulting in azero level output 639. The phase shift of π/2 radians between beams 629and 623, causes subtraction when the combiner 621 is a directionalcoupler. For a y-junction-based combiner 621 the phase difference shouldbe π radians.

When a signal 647 containing a coincidence pulse and artifact passesthrough the configuration of FIG. 12A, the incoming signal 641 isdivided into duplicate copies 649 and 651 (except for energy loss in thesplitting) one of which is amplified, by amplifier 615, to produce ahigher-level signal 655 with additional phase shift of π/2 radians.However, in this case, as the coincidence pulse passes through, theoptical amplifier saturates, thereby limiting the level of the copy ofthe coincidence pulse in the applied signal 651. The output 655 is thenattenuated, by attenuator 617, and coherently added with opposite phaseto the other copy 649 resulting in only partial cancellation. Only theportion of the coincidence pulse exceeding the saturation input levelremains in the output signal 659 and the artifact is canceled. Amplifier615 may not maintain the same phase shifts for both linear region 615Band saturated region 615A, resulting in a substantial outputcancellation for the artifact pulses and enhanced output of thecoincidence pulses that exceeded the saturation level of amplifier 615.

The configuration of FIG. 12A can be simplified by removing attenuator617 and adjusting the design of asymmetric combiner 621 to combine onlya small fraction of signal 627 with signal 623 (with opposite phases).Combining only a small fraction of the signal 627 with signal 623 isequivalent to the attenuation of attenuator 617. Thus, when usingasymmetric combiner, attenuator 617 can be removed while maintaining thefunctionality of the configuration in FIG. 12A.

To assure that the coincidence signal 647 of FIG. 12E, at path 627, willbe able to drive amplifier 615 into a saturation state, amplifier 616may be placed at the input to gate 614. In such a case, the saturationlevel of amplifier 616 may be chosen to be much higher than thesaturation level of amplifier 615, so amplifier 614 will allow amplifier615 to be driven into saturated state by the coincidence portion ofsignal 647.

It should be understood that the cancellator of artifact pulses (oroptical threshold device) 690 of FIG. 12A or its modified version ofFIG. 12G, as described below, may be located in close vicinity tocoincidence gate 614 to form an optical logical AND gate. However,optical threshold, such as device 690, may be a part of a customers' endunit, connected to an optical communication network where the networkincludes coincidence gates 614. In such a case the threshold device maybe located far away from coincidence gate 614 and may be separated fromgate 614 by multiple switching layers.

Referring to FIGS. 12F and 12G, an alternative method of artifactelimination (thresholding) employs an amplifier 582B with a gaincharacteristics in which output phase varies with input amplitude. Herethe substantially linear region 544B (idealized version shown at 544F)of the gain curve with regions 544C and 544G may be used for bothamplifying both artifact and coincidence signal. Near the “knee” of thegain curve, a region 544G is characterized by nonlinear amplification inwhich the phase of the output signal in this region 544G shifts by rradians relative to the output in the lower and linear regions of thegain curve 544C. The phase shift that is produced in region 544Grelative to linear region 544C depends on the relative change, in theindex of refraction, between these regions and on the length of theamplifier 582B. The flat region 544A beyond may or may not used.

An attenuation 582C may or may not be used to attenuate the energyreceived from amplifier 582B depending on design characteristics of thecircuit. Combining, in coupler 582E, only a fraction of the energyreceived from amplifier 582B is equivalent to attenuating this energyprior to its entrance to coupler 582E. For example, a combiner 582E maycouple a chosen fraction of energy from the output signal of amplifier582B into port 582D so that a corresponding amount, or no, attenuationmay be required. The amplified signal and original signal are combinedby a combiner 582E to generate an output.

The result of using the amplifier 582B is illustrated in FIGS. 12H and12K. The signals of FIGS. 12H and 12K are illustrated by a scheme wherea signal with a or radians phase shift is drawn upside down. Here theinput signal 546A includes only artifact and no coincidence pulses. Aportion 546C of signal 546A is amplified to produce signal 546D and thencombined, with the other portion 546B of original signal 546A having πradians out of phase with it. The amplitude range of the input signalfraction 546A is chosen so that artifact always lies below a point atwhich a phase of the signal 546E results in a cancellation as shown(FIG. 12H). That is, the intensity levels of the artifact pulses and thecoincidence pulses are adjusted to be in the linear gain region 544C andin the nonlinear region 544G, respectively. The same amplitude range isalso chosen such that the behavior illustrated in FIG. 12K is exhibitedwhen an input signal 545A having a coincidence pulse level is incident.Again, a portion 545C of input signal 545A is amplified to producesignal 545D. The non-coincidence pulses 545H (typ.) are combined, withtheir corresponding non-coincidence pulses in other portion 545B oforiginal signal 545A, having π radians out of phase with them. But now,the amplification of the coincidence pulse 545G results in a phasechange relative to the lower level portions 545H (typ.) of the samesignal (which include artifact). As a result, the coincidence pulse isenhanced, as indicated at 545F, by the summation and the artifact iscanceled. To assure that the intensity of coincidence pulse 545G will bein the non linear gain region 544G, the embodiment of FIG. 12G mayinclude an amplifier as part of the combined structure.

The amplifier 615 of FIGS. 12A and 582B of FIG. 12G need not necessarilybe different structures, as will be recognized by persons skilled in thefield of optical amplifiers. They may simply be the same type ofamplifier operated in different modes, one in which the saturated regionmay be used in which other may not. The use of the operation mode whichincludes the saturated region has the advantage that there is no need toaccurately adjust the phase relations between the artifact and thecoincidence pulses. The operation mode that does not include thesaturated region 544A has the advantage of being potentially faster andproducing higher intensity of output signals 545F.

Note that the amplifier 582B may also be replaced by a material or NLEwhose properties are such as to produce a phase shift that isproportional to the intensity. The latter may include an amplifier aspart of the combined structure. For example, such a nonlinear propertymay be employed by choosing a material and signal level such that thehigh energy level of the coincidence pulses, produce refractive-indexchange that will be resulted in a phase inversion relative to theartifact pulses having lower intensity level.

From the observation of the transmission-function shown in FIG. 12F itwill be observed that it is similar to that of an optical-limiter. Anoptical limiter is a device that has a linear (or close to linear)transmission curve, such as region 544B, corresponding to low signalintensities, a saturated region, such as region 544A, corresponding tohigh signal intensities, and a transition region, such as region 544G.Optical limiters are usually produced from materials whose opticalproperties, such as, index of refraction, scattering, or absorptionchange under high radiation intensity and are used to limit the outputintensity of the device at high intensity levels. Accordingly amplifier582B can be replaced, without affecting the above-described operation,by an NLE or any other limiter device that has a transmission curvesimilar to that shown in FIG. 12F In such a case the optical limiter,similar to amplifier 582B, can be operated in the two above mentionedmodes, i.e., one in which saturation region 544A is used and the otherin which it is not.

Referring now to FIGS. 16E and 16F, another way to enhance coincidencepulses relative to artifact at the receiver is to use a comparator(differential amplifier) 990 to subtract the power of the coincidencesignal 993C from that of the non-coincidence signal 993D emanating fromgate 993. Coincidence and non-coincidence signals 993C and 003D,respectively, are incident on respective detectors 993A and 993B. Thedetectors 993A and 993B are insensitive to the phase of the E-field andconvert the energy of optical signals to electrical signals and theresult is applied to the different inputs 990A and 990B of a comparator990. Signals 993C and 993D are illustrated by a scheme where E-fieldswith or radians phase shift are drawn upside down. At the output 990C ofthe comparator 990, the coincidence pulse remains but thenon-coincidence, or artifact, pulses are canceled as shown withreference to FIGS. 16E and 16F. It will be recalled that when a signalis incident alone on a gate 993, such as gate 100 of FIGS. 1A–1D, thepower profiles include only artifact pulses and no signal will beproduced at output 990C of comparator 990. Exemplary signals are shownat gate 993 outputs 991A and 992A of FIG. 16F with a coincidence pulse991C and artifact pulses 991B (typ.) emanating from the coincidenceoutput 991A and only artifact pulses 992B (typ.) emanating from thenon-coincidence output 992A. The signals at outputs 991A and 992A areillustrated by their intensity with no indication to the phase of theirelectrical field, in a way similar to the way that they are detected bydetectors 993A and 993B of FIG. 16E. It may be confirmed by inspectionthat when the corresponding electrical signals are applied to the inputsof a comparator 990 of FIG. 16E, with suitable synchronization, that theelectrical signal portions corresponding to the non-coincidence pulses9911B (typ.) and 992B (typ.) will align and cancel but that theelectrical signal portions corresponding to the coincidence pulse 991Cwill not. Thus, the output of the comparator 990 will be as indicatedfiguratively at 994.

It should be understood that detectors 993A and 993B and comparator(differential amplifier) 990 may be located in close vicinity tocoincidence gate 993 to forms a logical AND gate. However, detectors993A and 993B and comparator 990 may be part of a customers' end unit,connected to an optical communication network where the network includescoincidence gates 993. In such a case detectors 993A and 993B andcomparator 990 may be located far away from coincidence gate 993 and maybe separated from gate 993 by multiple switching layers.

Referring now to FIGS. 22A and 22B, another mechanism for enhancing theratio of coincidence signals to artifact is to provide a trailing pulsethat coincides only with the coincidence pulse, thereby enhancing itfurther relative to the artifact, but producing artifact that still hasthe same maximum level. In FIG. 22B, a first pulse-pair 1142 defines asymbol by which a coincidence pulse can be generated by a firstsummation using a gate 1125 indicated in FIG. 22A. A third pulse 1141Acoincides with the coincidence pulse, produced by gate 1125, in a secondsummation that occurs in a following gate 1126 (FIG. 22A) after thefirst summation (as provided by a delay line 1123 of Δt₂, shown in FIG.22A), which produces the coincidence gain, thereby enhancing the firstcoincidence pulse produced by the first gate 1125. The second summationcan be the summing of the output of a first summation with a signalproportional to the original signal (i.e., a duplication of it).

Referring to FIGS. 22A and 22C, first, an original signal 1130 isapplied at an input of a first Y-junction 1129A which splitsapproximately 1/3 of the input energy into a first branch 1123 sending2/3 into an input of a second Y-junction 1129B which forms part of agate with second and third delay branches 1121 and 1122. The difference(Δt₁) between the delays of the second and third delay branches 1121 and1122 causes a coincidence pulse at an output of a first reverseY-junction 1125 if that difference matches the delay between the twopulses defining the symbol 1142. Copy 1131 of signal 1130 is delayed atbranch 1121 by a time difference of Δt₁ compared to signal 1130 ofbranch 1122. Signal 1132 show the output at Y-junction 1125 afterexperiencing second and third delay branches, having a time delaydifference of Δt₁. Signal 1132, now flowing into reverse Y-junction1126, is summed with the signal of branch 1123, which experienced a Δt₂delay. Copy 1133 of signal 1130 is delayed at branch 1123 by a timedifference of Δt₂ compared to signal 1130 of branch 1122. Signal 1133has a delay that causes the duplicate of the pulse 1141A in the originalsignal delayed to sum with the coincidence pulse 1136 of coincidencesignal 1132 in second Y-junction 1126. The output at 1126 is shown at1134 and is the result of summing signal 1133 (delayed original signal)with the output at 1125 creating a larger coincidence pulse 1137 in thefinal output 1134. An enhancement device 1127 of FIG. 22A like thatshown and described, for example with reference to FIGS. 10D and 10E,may further enhance the coincidence pulse. The enhancement may beprovided by any number of enhancement pulses in similar branches withcorresponding delays as indicated at 1124 with the ellipses shown.

It may be observed by inspection that suitable delays need to beincorporated after each symbol including its enhancement pulse toprevent inter-symbol interference. This may be necessary also to preventundesired interaction in other gates used in the same system (notshown). The precise length of the required guard band will depend on themodulation scheme employed.

Note that junctions 1129A and 11 29B may be combined into a single starjunction and gates 1125 and 1126 can be implemented as a singlecombiner, the particulars of the embodiment of FIG. 22A having beenchosen for illustration purposes.

Each branch 1124 (typ.) in the device of FIG. 22A forms a coincidencegate with another branch 1124 (typ.) and has its specific enhancementpulse. Accordingly the device of FIG. 22A may represent a combinedcoincidence gate including multiple coincidence gates connected inparallel. Such a combined coincidence gate responds, to form maincoincidence signal, only for a specific symbol constructed by specificspaces between its pulses that match the specific combined gate andrepresent a specific address (predetermined destination). Such a symbolincludes multiple pulses with a number of pulses greater than two. Themain coincidence signal is the coincidence pulse with the highestintensity that exists in the system for a specific symbol. Due tointer-symbol coincidence events, some other coincidence signals may beproduced in any gate. Still, the main coincidence pulse is the pulsewith the highest intensity produced in the system. This highest levelmain coincidence occurs only at a specific gate that matches the timedelays between the pulses of a specific address of a specific symbol.

It should be clear that the symbols that include multiple enhancementpulses may be used as multiple control pulses. In such a case theaddress (destination) of the symbol is determined by the specific timespaces between the multiple control pulses and the data pulse in thesymbol. The enhanced coincidence pulse, discussed above, is in this casea main coincidence pulse, produced by a specific combined gate thatresponds to this specific symbol.

The combined coincidence gate may be constructed from parallel multiplegates, each responding to a different time space between the pulses ofthe symbol. Each parallel coincidence gate that constructs the combinedgate, may be identified by any number, greater than two, of delaybranches 1124 (typ.) of FIG. 22A. For example, the shortest delay branchmay be a common branch for all the parallel gates. In this specificexample, the branch with the shortest delay together with any number(including 1) of parallel branches 1124 (typ.) may represent oneparallel gate. The data pulse and the control pulses in the symbol canbe identified arbitrarily.

From FIG. 22C it can be seen that when no threshold mechanism is used,the combined coincidence gate may produce artifact pulses(non-coincidence or non-main coincidence pulses) that may interfere withthe pulses of the next following symbol to produce unwanted coincidencepulses. To avoid the creation of unwanted coincidence pulses, a timeguard band should be maintained between the data symbol signals. The useof such guard bands reduces the efficiency of the informationtransmission.

FIGS. 22D, 22E and 22F illustrate a demultiplexing system thateliminates the need for time guard bands, the closely packed datasymbols, and the combined coincidence gates used to demultiplex thecomplex multiple pulse symbols.

Referring to FIGS. 22D and 22F, FIG. 22D illustrates a demultiplexingsystem 3000 designed to receive and demultiplex signals of data symbols3040, illustrated by FIG. 22F, arranged within time frames 3046 (typ.)The use of demultiplexing system 3000 eliminates the need for guardbands between the symbols. Demultiplexing system 3000 of FIG. 22Dincluding multiple combined coincidence gates 3024A–3024N constructed bya combination of parallel and series connections between discretecoincidence gates 3012A–3012N, 3014A–3014N and 3020A–3020N,respectively. It can be seen that coincidence gates 3012A and 3014A areconnected in parallel and each of them is connected in series tocoincidence gate 3020A.

Signal 3040 of FIG. 22F is received at input 3002 of system 3000 of FIG.22D. Dividing device 3004 splits signal 3040 and simultaneously emitcopies of signal 3040 into ports 3006A–3006N. Ports 3006A–3006N are alsothe inputs of combined coincidence gates 3024A–3024N having respectiveoutput ports 3022A–3022N.

Referring momentarily to FIG. 22F, illustrating signal 3040 constructedby time-frame pulses 3042 (typ.) (shown with diagonal hatch filling) andinformation pulses 3044 (typ.) (shown with clear filling). Time frames3046 (typ.) includes time slots 3050 (typ.) and are constructed, forexample, by the space between pulses 3042A (typ.) and 3042B (typ.).Information pulses 3044 (typ.), located within frames 3046 (typ.)between pulses 3042A (typ.) and 3042B (typ.), are spaced apart by anintegral number of timeslots 3050 (typ.).

Each pulse 3042 of time frames 3046 has double duty to serve both, as areference pulse for the currently demultiplexed time frame 3046 and as acontrol pulse for the next following time frame 3046. Signal 3040propagates in the direction shown by arrow 3048 thus, delayed pulses3042A and leading pulses 3042B (ahead in time) may serve as thereference and the control pulses for the currently demultiplexed timeframe 3046, respectively. Pulses 3042A may also serve as the referencepulses for the leading information pulses 3044 to create data symbolsformed by the time delays Δt₁–Δt_(n) between pulses 3044 and 3042A.Delays Δt₁–Δt_(n) are equal to the delays of coincidence gates3012A–3012N in combined coincidence gates 3024A–3024N, respectively. Thetime delay Δt_(F) between pulses 3042A and 3042B of frames 3046 is equalto the time delay of gates 3014A–3014N of combined gates 3024A–3024N,respectively. All frames 3046 are closely packed and do not include timeguard bands between them.

Referring now back to combined gate 3024A of system 3000 of FIG. 22D.The analysis for gate 3024A represents the process occurring in allcombined gates 3024A–3024N, and thus only gate 3024A will be discussedwithout repeating the analysis for the rest of the combined gates. Thecopy of signals 3040 at inputs 3006A of combined gate 3024A is copiedagain, by radiation guides 3008A and 3010B, into coincidence gates 3012Aand 3014A, respectively. Gate 3014A produces a coincidence signalrelated to frame pulses 3042 (typ.) every time period equal to delayΔt_(F). Gate 3012A produces a coincidence signal only where the timespace between information pulse 3044 (typ.) and reference pulse 3042A isequal to Δt₁. The coincidence signals from gates 3012A and 3014A arefeed into the inputs of coincidence gate 3020A that produces outputsignal at output port 3022A of combined gate 3024A only if thecoincidence signals from gates 3012A and 3014A arrive to gate 3020A witha delay equal to delay S_(A) of gate 3020A.

Note that if the total length of the optical path through guides 3008A,gate 3012A and guide 3016A matches the total length of the optical paththrough guides 3010A, gate 3014A and guide 3018A, then delay S_(A) ofgate 3020A may be equal to zero. Assuming, without any limitation, thatS_(A)=0. In such a case, for producing coincidence signal at output port3022A, the coincidence signals of gates 3012A and 3014A should occursimultaneously. Simultaneous coincidence at gates 3012A and 3014A canoccur only with information pulses 3044 (typ.) related to the currentlydemultiplexed time frame 3046. Information pulses 3044 related toadjacent time frames 3046 are delayed from reference pulses 3042A by atime space that is greater than the largest delay Δt_(F) in system 3000and thus can not produce a coincidence pulse in gate 3012A at the sametime gate 3014A produces a coincidence.

Accordingly, similar to the discrete coincidence gates in thedemultiplexing systems of FIGS. 14A–14D discussed below, combined gate3024A produces output signals only for symbols having a time delay equalto its time delay Δt₁. However, unlike the system of FIGS. 14A–14D,demultiplexing system 3000 prevents any unwanted coincidence signalsbetween the pulses of different time frames even where there is no timeguard band between time frames 3046.

FIG. 22E illustrates coincidence gate 3024M having alternative structureto the structure of combined gates 3024A–3024N. In combined coincidencegate 3024M of FIG. 22E, gates 3012M and 3014M are connected in paralleland both of them are connected in series to gate 3020M. Combined gate3024M may produce results similar to combined gates 3024A–3024N wheneverdelay Δt_(X) of gate 3020M is adjusted to be equal to the relative delaycaused by the different lengths of the optical paths from port 3006M toport 3022M, via gates 3012M and 3014M, respectively. Gates 3012A, 3014Aand 3020A of FIG. 22D have similar functionality as gates 3012M, 3014Mand 3020M, respectively.

It should be understood that coincidence gates 3012A–3012N, 3014A–3014N,3020A–3020N, 30012M, 3014M and 3020M are all of the various types ofcoincidence gates 101 of FIG. 13I discussed below, For example they mayor may not have a threshold mechanism or may have electrical or opticalthreshold devices. In a situation where gates 3012A–3012N, 3014A–3014N,3020A–3020N, 30012M, 3014M and 3020M have no threshold mechanism, theinformation demultiplexed to designated ports 3024A–3024N is identifiedby main coincidence signal. The main coincidence signal is the signalwith highest intensity in the system. Other coincidence signals mayexist either in the same designated gate in which the main coincidencesignal is produced or in any other gates of system 3000, but these havelower intensity than the main coincidence signal.

It should also be understood that all the discrete coincidence gates ofthe demultiplexing system related to the present invention such as thedemultiplexing system of FIGS. 14A–14D and 15K–15R including thecross-connection box of FIG. 15S may be replaced by combined coincidencegates, such as the combined coincidence gates illustrated by FIGS. 22Dand 22E. Such combined coincidence gates may include any combination ofparallel and series connections between discrete coincidence gates.

Note that the data symbol signals for the combined coincidence gates ofsystem 3000 include time-frame pulses 3042A (typ.) and 3042B (typ.) andinformation pulses 3044 (typ.) thus is constructed by more than twopulses. The number of pulses that may be used in the data symbol signalsincreases with the number of discrete coincidence gates used toconstruct the combined coincidence gate that uniquely decodes the datasymbol signals.

A variety of embodiments of a gate 100 were discussed previously andwill be summarized presently along with some others. As shown in FIG.13A, a gate mechanism 605 which may be any device that accepts inputsignals at input ports 601, 603 and generates output signals at outputports 606, 608 such that at least one of the output signals isresponsive to an interaction between the input signals and preferablywithout requiring a change of state of gate mechanism 605. The inputsignals A and B may come from a variety of sources and the outputsignals C and D may be conditioned in a variety of ways to achieve oneor more final outputs. As will become clear from the detaileddescription below gate, 100 may be used as a decoding device as well.

For example, referring to FIG. 13B, the inputs A and B may be fromindependent sources such as an incoming information signal 607 from aremote sender (not shown) and a local external signal from a localcontroller 604. In such a case, a synchronization and phase recoverycontrol loop may be incorporated in the configuration as shown in FIG.13B. Various processes for synchronization and phase recovery arediscussed in the following sections.

Referring now to FIG. 13C, a portion 604G of the output signal 604E fromoutput 608 (designated C) of gate 605 of FIG. 13A is coupled out, bycoupler 604F, and is sent to a detector 604A. Detector 604A generates anelectrical signal to be transmitted, via electrical lead 604D, tocontroller 604. Controller 604 drives actuator 604B via electrical lead604I. Controller 604 and actuator 604B drive a wedge prism 604C. Themovement of wedge prism 604C in the directions indicated by arrows 604Jchanges the optical path of signal 604H to control its phase. Themovement of prism 604C changes the phase of the input signal 604Happlied to one of the input ports 601 or 603 (designated A or B,respectively) of gate 605 of FIG. 13A to change the relative phases ofthe signals incident on ports 601 and 603. This function ofphase-alignment may be accomplished by various means, here figurativelyillustrated by a wedge of material 604C with a different index ofrefraction from upstream or downstream media. The detector outputs thesame or another signal at electrical lead 604D for synchronizationrecovery which is applied to the controller 604 to synchronize theoutput of the local signal with that of the incoming signal. The signalat lead 604D may be one that is responsive to the precise coincidence ofaligned pulses. Controller 604 controls stage 604B that moves wedgeprism 604C along arrows 604J. The movement of wedge prism 604C in thedirections 604J changes the optical path of signal 604H to control itsphase. The described construction is a closed-loop scheme that maintainsthe synchronization of the local signal and the incoming signal overtime.

The mechanical phase-shifting technique described with reference to FIG.13C may be replaced by any suitable mechanism. Referring now to FIG.13D, a controller 724 sends an actuation signal to a phase shifter 720,essentially any kind of transmission component that changes its delay oftransmission by a phase angle according to the applied signal. Thesignal may be a feedback control based on a signal from a sensor device730. One example of a sensor device 730 is illustrated. A client device725, receives signal energy phase-shifted by the phase shifter 720. Theclient device 725 may be, for example, a gate. A beam splitter 722captures some of the energy output by the client device 725 and appliesthis sample signal 727 to a detector 723. The detector 723 generates anelectrical signal indicating the intensity of the sample signal 727 forexample by time-integrating the signal and outputting an average or RMSpower level indication thereof or by detecting and latching a peakintensity or by any suitable means. The signal generated by detector 723is transmitted via electrical lead 727A to controller 724. The phaseshifter is driven by controller 724 according to the signal produced bydetector 723. The phase shifter may include various means for changingphase such as by means of an electric field or thermal effect or amechanical mechanism 604B/604C as discussed with reference to FIG. 13C.A piece of material whose index of refraction changes with appliedelectric field or temperature may be activated by a device that appliesan electric field or a heater. Alternatively, different delay lines maybe electronically switched in and out of a signal path to generate acumulative selected delay.

The client output signal 719 emerging from the beam splitter 722 is usedin a system requiring the phase compensation provided by the phaseshifter 720. Alternatively, the whole control apparatus of FIG. 13D maybe used to generate a control signal for a series of clients in whichthe client 725 is a model.

Referring now to FIG. 13E, a phase recovery device 728 encapsulates thefunctionality of sensing the signal phase alignment, for example, 722,723 and 724 of the embodiment of FIG. 13D. A phase shifter 729 maycorrect the phase angle for all recipient clients 731A–731C connected toa distributor 742 and a model client 731Q. Alternatively, phase shifters(not shown) internal to each of the clients 731Q and 731A–731C may becontrolled instead, depending on the type of device that is used for theclients. The model client 731Q has properties as recipient clients731A–731C and therefore the correction for client 731Q would betherefore correct for clients 731A–731C. For example, 731A–731C and 731Qmay be of the same materials and maintained at identical environmentalconditions. The properties of 731Q need not be identical to those of731A–731C, but the compensation may be derived from the changes in thephase required to compensate 731Q. For example, if each client has agate with a delayed input and a non-delayed input, the delays of eachgate may need to be compensated differently and therefore the correctionmay need to be applied to a phase shifter (not shown) internal to eachgate.

An example of a client, e.g. 731A, is a gate 101 as described below withreference to FIG. 13I, which may have a gate 100 with a particulardelay. As will become clear from the detailed description below gate 101may be used as decoding device as well.

The process of synchronization and phase recovery may be reserved to aregular calibration process that is done at intervals sufficient toensure the phase and synchronization remain proper. It is assumed thatthe processes upstream of the ports 601 and 603 of FIG. 13A (or anyports of gates described anywhere in the instant specification in whichcoherent summing takes place) are synchronized with a system such as thesystem of FIG. 13D by this process and they only fall out of synch andphase alignment due to slow drift processes. Thus, the above method isnot suggested as being suitable for the instantaneous recovery of phaseand timing alignment of asynchronous signals.

Referring to FIG. 13F, the inputs A and B may also come from a singlesource 607 that has been split by a splitter 602 with one input A havinga different time-delay from the other B. As indicated, a selector device600A may be provided to choose among multiple time delay components600B, 600C and 600D to allow automatic selection of the time delay. Thetime-delays selection may be performed remotely. A time-delay selectoris schematically illustrated and described below by FIG. 13J.

FIG. 13J is a schematic illustration of a configuration for a time-delayselector 700, which may be used, for example, for selector device 600Aof FIG. 13F. Selector 700 includes m subunits 702 (typ.), each of whichincludes n delay lines 704 having respective delays. An input signal 708is directed to a controllable mirror 706, such as controlled by a MEMSswitch, which may be controlled locally or remotely. Mirror 706 directsa reflected signal 710 to one of delay-lines 704 of a first subunit 702Awhich relays it to mirror 714, which is also controlled. Mirror 714reflects the signal to mirror 716, from which further redirects thesignal into another subunit 702B and the process is repeated with mirror716 directing the signal through a selected delay and mirror 718relaying to another subunit 702C and so on. Each subunit 702 provides ndifferent delays. With m subunits 702, each having n delays, selector700 may select n^(m) delays for a final output 717. Of course, althougheach subunit 702 is shown with n delays, it is possible for each to havea different number of delays. Note that the most effective use of thestructure 700 is to have one of the subunits 702, for example the firstsubunit 702A, provide course delays, with each successive subunit 702B,etc., providing successively finer levels of delay.

Referring to FIG. 13G, signals C, D from one or both of the outputs,such as of FIG. 13A, individually or together, may be conditioned by aprocess to enhance the distinctiveness of information symbols relativeto artifact. For example, one or both outputs may be combined coherentlywith a signal from a CW laser 611 via a summer 609 to generate aconditioned output 614A.

Referring to FIG. 13H, the output signals C and D may also beconditioned to eliminate artifact entirely by the process described withreference to FIGS. 12A–12K. That is, one or both outputs, together orindependently, may be applied to such a filter as described withreference to FIGS. 12A–12K, illustrated symbolically at 583A to yield afiltered signal 583B.

Referring to FIG. 13I, to facilitate the discussion of the applicationof such embodiments, given that a variety of embodiments may all beemployed in each application, an iconic representation of a gate 101 maybe used in the remainder of the instant specification to identifyvariations of such gates that may be used as coincidence gates anddecoding devices. The iconic representation of a gate 101 (or hereafter,simply “gate”) has two inputs 614 and 616 which may correspond to any ofthe inputs A, B, 601, 603, 604 or 607 represented above in FIGS. 13A–Hor others and two outputs 610 and 612, which may represent either of theoutputs 606, 608, C, D, 614A or 583B in FIGS. 13A–13H or others. Asymbol–selection symbol S_(n) indicated by 101A may be placed on theface of the gate 101 to identify a characteristic that selects foroutput at a predetermined output only one of multiple symbols. Forexample, it may represent one of a set of time delays of respective timedelay devices such as one of 600B, 600C, or 600D (FIG. 13F). In thatcase, the gate 101 may be taken to represent one with a single inputthat is split with one being subject to a time delay to make a symbolselector as discussed with reference to FIG. 9B. The label S_(n)indicates the symbol that selects the channel, for example, usingmodulation based on polarization, phase, time delay Δt_(n) etc. or acombination thereof.

It should be understood that gate 101 may represent any combination ofcoincidence gate 100 with or without its accompanied means describedelsewhere according to the present invention. Such a combination mayinclude coincidence gate 100 with more than one accompanied means. Forexample, gate 101 may include gate 100 with or without optical thresholddevice, contrast enhancers of various types used to enhance to increasethe ratio between coincidence and non-coincidence signals or background,variable time delays, closed loop phase controls, closed loop clockrecovery control, and other means described according to the presentinvention.

It should be noted that the inputs of gate 101, input 614 and input 616are also schematically designated as lettered circles A and B. Theoutputs of gate 101, output 610 and output 612 are also schematicallydesignated as lettered circles C and D. This notation shall be usedthroughout the various illustrations.

Referring to FIG. 14A, gate 101 may be applied in a variety ofcommunications systems, a simple one of which may employ a demultiplexer(encoder) 640. FIG. 14A illustrates the use of coincidence gate (orgate) 101 as a decoding device for decoding encoded data symbols 638A(typ.) in multiplexing system 640. It should be understood that in everydemultiplexing system according to the present invention coincidencegates (or gates) 100 and 101 may represent decoding devices as well. Aninput signal line 638 (designated B) carries a signal 638A (typ.) with amix of symbols such as spaced-pulse symbols as illustrated. Signal 638Ais distributed among N gates 622 (typ.), by dividing device 644, withdifferent characterizations S_(n) (e.g. time delay) selectors (not shownexplicitly) therewithin, for example time delay Δt_(n) symbol selectorsas indicated. The signal is modified by the action of the respectivegates 622A, 622B, 622C and 622D. The resulting respective signalsillustrated at 624A, 624B, 624C and 624D each include a coincidencesymbol, in this case a pulse 626A, 626B, 626C, 626D, only for symbolscorresponding to the symbol the respective gate 622A, 622B, 622C and622D is configured to select. The signals 624A, 624B, 624C and 624Dinclude at least one coincidence pulse, 626A, 626B, 626C and 626D andartifact, for example as indicated at 628. However and withoutlimitations, signals 638A and gates 622A–622D may be selected in a waythat results with no coincident signals. Note that the artifact 628(typ.) may or may not be present depending on the configuration of thegates 622A, 622B, 622C and 622D. For example, a gate that isincorporated with the device, shown in FIG. 13H, designed to opticallycancel the artifact pulses will not produce artifact pulses such aspulses 628. Each signal 624A, 624B, 624C and 624D is sent to arespective destination D₁, D₂, D₃ and D_(N). The destinations mayinclude receivers (not shown) that are selectively responsive only tothe high intensity coincidence symbols 626A, 626B, 626C and 626D. As aresult, in effect, only the coincidence symbols are received by thereceivers and the data is, by definition, demultiplexed by this scheme.

It will be observed that the system may be configured such that thespacing of the coincidence symbols 626A, 626B, 626C and 626D is higherthan the spacing of symbols in the signal 638A, not only by virtue ofhaving been stripped of the pulse-spacing symbology, but, moreimportantly, as a result of reduction in the duty cycle (and therefore,the data rate) of each channel 642 (typ.) and therefore a reduction inthe duty cycle of each receiver. As a result, if the spacing of symbolsin the signals 638A is too low for any receiver to handle, for example,a receiver with an optical to electrical signal conversion process thatincludes transfer to storage, the incoming signal 638A will be dividedamong multiple parallel signals 624A–624D, providing a slower symbolrate in each than the combined signal 638A allowing the receivingprocesses to occur in parallel. Note that the signal 638A maynecessarily lose intensity as a result of being divided among multiplechannels and this may be compensated for by inclusion of an opticalamplifier, in input B (not shown), without changing the operation of thedevice.

It should be clear that system 640 is a self demultiplexer thatdemultiplexes the information pulses in the symbols of input signal638A. Each symbol of signal 638A includes an information (data) pulseand a control pulse. The self demultiplexing of the information in thesymbols of signal 638A is performed by producing a coincidence pulse ina specific designated port (destinations D₁–D_(N)) that is responsiveonly to a specific predetermined destination encoded in the inputsymbols constructed by selecting the time space between the information(data) pulse and the control pulse.

Divider device 644 may represent any means for distributing the inputsignal from one input into multiple ports. Device 644 may be, forexample, a star splitter/coupler, a cascade of one-to-twospliters/couplers, a cascade of one-to-many splitters, a loop havingmultiple ports, and a combination between all the means above.

FIGS. 14B, 14C and 14D illustrate the system of FIG. 14A when showing,for example, several of the interior optional structures of divider 644.FIG. 14B shows, for example, device 644 that is constructed from a starsplitter 641A including ports 622E–622H. FIG. 14C illustrates, forexample, device 644 that is constructed from a cascade of one-to-twosplitters 641B, 641C and 641D having ports 622I–622N. One-to-manysplitters 641B, 641C and 641D of FIG. 14C may be of the type of starsplitters, directional couplers, or Y-junctions. FIG. 14D illustrates,for example, device 644 that is constructed from loop 644A includingmultiple splitting ports 622O–622R.

It should be clear that while some of the splitters in FIGS. 14B, 14Cand 14D are illustrated as one-to-two splitters, they may representone-to-many splitters as well.

Referring now to FIG. 15A, a simple mechanism for creating time pairsymbols 820 with different time separations is to provide two paralleldelays 816 and 817 to which a single data pulse 812 is applied. Thedifference between the time delays of delays 816 and 817, hereillustrated as fiber loops, determines the pulse spacing of theresulting symbol 82U. Referring to FIG. 15B, a parallel delay device asillustrated in FIG. 15A may be represented by an iconic representationof a symbolizer 818, which may have an indicator representing a uniquesymbol, such as a unique magnitude of the pulse spacing produced. Asignal 819 passing through the symbolizer 818, characterized by a delayΔt_(n), is converted into, or attached to, a symbol resulting in alabeled symbol 821, for example a pulse-pair, spaced by a delay Δt_(n),as illustrated. In some embodiments, a symbolizer is also referred to asa duplicator.

Referring now to FIG. 15C, a multiplexer 800 places the signals from sixseparate data channels onto a single data channel that may be in form ofTime Division Multiplexing (TDM) in which each TDM channel is “labeled”with a different symbol. Thus, a demultiplexer such as 640 in FIG. 14Amay be used to distribute the multiplexed signal among six parallelchannels each receiving and processing data at a lower rate. A modelocked laser 803A is used as a source of narrow pulses. It ischaracteristic of mode locked lasers that they produce outputs of narrowpulses with relatively long delays as illustrated by signal 804 at theoutput of laser 803A. The mode locked laser 803A output is distributedby a splitter 808 to six channels 808A (typ.), each with a respectivetime delay as indicated at 805 (typ.). A modulator 806 (typ.) on eachchannel 808A (typ.) determines whether a pulse is passed on that channelor not in response to a control signal from a respective data source 801(typ.), such as sources S₁–S₆. A respective symbol is applied to thesignal on each channel 808A (typ.) by a respective symbolizer(duplicator) 818A (typ.). The resulting output signal 807 is illustratedat output 809 and may include a highly dense series of pulses in a formof numerous symbol signals that may be distributed in a form of TDM. Theduplicator 803D represents an arbitrary number of implicators connectedin series, parallel, or any combination of serial and parallelconnections and having situations delays. The symbolizers included inand represented by symbolizer 803D may optionally be added to so thatthe delay between pulses of the mode locked laser 803A may be matchedagainst the number of channels 808A (typ.) by duplicating the pulses therequired number of times. This may be done, as indicated, by means ofone or more duplicator 803D, which includes a summer and suitable delays(not shown in the present drawing, but described by FIGS. 15A and 15Band elsewhere) to make any required density of pulses in the signalprior to being split by the splitter 808. A synchronization recoverycircuit 803B may be provided to ensure that the modulators 806 (typ.)are controlled such that the signals from data sources 801 (typ.) areproperly synchronized with the output of the mode locked laser 803A. Forexample, a synchronization signal 811 may be generated by a detector in803B that receives a small portion of the signal that laser 803A emits(not shown separately).

Note that instead of using a single mode locked laser to form a streamof pulses to multiple modulators, signals can be obtained from multiplemode locked lasers with a common cavity such that their signals aresynchronized.

Note that six data channels have been chosen for illustration purposesonly. This number, six, is chosen arbitrarily and has no practicallimitation to the number of data channels (along with respective delays,modulators and symbolizers) that can be used.

In another alternative, a single mode locked laser 875 as shown in FIG.15D feeds a pulse-signal 875A into upper branch 879C of input 879B ofdirectional coupler 877D. Input branch 879C is coupled to upper andlower branches 879E and 879F of output 879A of coupler 877D. Lowerbranch 879F is connected, by loop 877, to lower branch 879D of input879B of coupler 877D. Loop 877 includes controllable delay loop 877A,amplifier 876, and gate 878. At a certain starting time, the firstpulse-signal 875E of signal 875A is received by the upper branch 879C ofinput 879B of coupler 877D. Directional coupler 877D divides the energyof the first and subsequent pulses 875E in signal 875A into an outputpulse propagating through branch 879E and a returned pulse propagatingtoward loop 877 via branch 879F. The part of energy of pulse-signal 875Athat is directed through output 879E appears as the first output signal.The other part of the energy of signal 875A enters into loop 877 whichsends its energy back to branch 879D in input 879B. The part ofpulse-signal 875A propagates along loop 877 (the returned signal) isamplified by amplifier 876 and passes through loop 877A and gate 878 toreturn to coupler 877D. The returned signal 875A that returned to branch879D, through loop 877, is divided, by coupler 877D into an outputsignal at the upper branch 879E and a returned signal directed back intoloop 877. This process may repeat itself in a steady-state condition toproduce a train of duplicated narrow output signals. To provide a steadytrain of pulses, the intensity of all the recirculated pulses should beequal to the first signal that entered loop 877. In addition the firstoutput signal, at branch 879A, should be equal to the next output pulsesthat follow after the delay imposed by loop 877. Thus, each fraction ofthe energy from each pulse 875E that leaves at 879E is followed byanother portion that has recirculated through the loop 877 resulting ina continuous train of pulses. The recirculating pulse may be amplifiedby an amplifier 876. A delay loop 877A determines the spacing between anexiting pulse and the following pulse that flows through the loop 877.The amplification of amplifier 876 and energy partitioning of couplingof directional coupler 877D are preferably such as to ensure the pulsesin the train exiting at 879E has substantially the same amplitude. Forexample, this may be obtained if coupler 877D is of a type characterizedby 50/50 power splitting and amplifier 876 has a gain that compensatesfor loop loss (including propagation and bend loss) and coupler loss(50%) to assure that the product between the combined effect of gain andthe overall attenuation loss of a round trip along the loop 877 is equalto one.

In a steady state, the process of duplicating the pulses by loop 877produces a train of identical narrow pulses. The process continues tillanother pulse 875E appears in signal 875A of mode locked laser's 875output. Just before the appearance of such pulse, gate 878 may be turnedactivated to stop recirculation of a returned signal (pulse) in loop877. After the termination of the pulse duplication and before thearrival of the next pulse 875E, gate 878 activated to block the pulsecirculating in the loop 877 and to allow the beginning of a newduplication process. Again this continues till the next activation ofgate 878 and the appearance of the next pulse of signal 875A. Gate 878can be a shutter, an LCD window, a coherent summer receiving light froma source such that the pulse in the loop 877 is canceled, or anysuitable device.

The interval between duplicated pulses is the time-space betweenduplicated pulses and is equal to the total delay of loop 877. To createa train of pulses equally spaced, the space between two following pulses875E of signal 875A should be equal to an integral number of spacesbetween duplicated pulses and the delay of loop 877 has to satisfy thiscondition.

Gate 878 is activated to halt the last pulse to be repeated before a newpulse is generated by the mode locked laser 875. Gate 878 is deactivatedto allow the passage of the new pulse generated by laser 875 whichpropagates in loop 877. Thus a narrower train of pulses 875B can begenerated at output port 879E with only one delay device. This may allowthe pulse train 804 (FIG. 15C) to be generated by the device of FIG. 15Dand to be arbitrary distances apart within the scope of integraldivisions of the spacing of the mode locked laser 803A (FIG. 15C).

Referring to FIGS. 15C and 15E, as mentioned, a demultiplexer usinggates such as indicated at 829 (typ.) may be used to distribute themultiplexed signal from point P, which is a common input point of thedemultiplexer of FIG. 15E and common output point of multiplexer 800 ofFIG. 15C among illustrated six parallel channels 824A–824F each with amatching detector 828 (typ.) receiving and processing data at acorrespondingly reduced rate. More particularly, the signal 807 frommultiplexer 800 is applied, after, for example a lengthy transmissionchannel such as a long-haul fiber, to a common input 824 which is thendistributed by means of a distributor 827 to the six channels typifiedby the channel indicated at 824A. Distributor 827 may represent anydistributor, for example, any distributor of the types 644 illustratedby FIGS. 14A–14D or discussed in their accompanied description. Thedemultiplexed signals, typified by the representation at 805, are thenconverted to electrical signals, by detectors 828 (typ.) and may beapplied to respective outputs 826A–826F, which may be electrical signalsor any other suitable medium. For simplicity, signals 805 areillustrated after gates 829 without any artifact. This may be the caseif the coincidence pulses are produced by gates 829 that produce noartifact, as in the embodiments of FIGS. 12A–12K. If otherwise, anycoincidence pulses may be distinguished from the artifact pulses by anelectronic threshold detector or comparator that may be incorporatedwithin the detectors 828 (typ.) Comparators that generate an output onlywhen a signal is above a predetermined threshold are staple electroniccomponents and their details need not be discussed here.

Here, as with FIG. 15C the number of six channels is chosen arbitrarilyand has no practical limitation to the number of data channels (alongwith respective gates and detectors) that can be used.

Referring now to FIGS. 15F and 15H, another way of forming extremelynarrow pulses is to apply a pulse broader than the desired narrow pulse,from a modulated laser source 851 (L indicates the laser, M indicatesthe modulator, and C indicates the clock) whose width is a wide Δt_(Y)to a gate 841 with a time delay equal to Δt_(X)=Δt_(Y)−Δt_(Z) to obtainpulses whose width are narrow Δt_(Z). Gate 841 splits the applied pulse839 into two copies 843 and 844 that are overlapping coincident only forthe duration of Δt_(Z), thereby determining the width of the resultingpulse 846. Gate 841 may be of the type of gate 101 that includes opticalthreshold mechanism such as shown in FIGS. 12A–12K. Accordingly, signal846A resulted from the delayed summing of copies 843 and 844 of originalsignal 839 appears as signal 846 after passing through the thresholdmechanism of gate 841.

Referring now to FIGS. 15G and 15H, a gate 841A that does not completelyeliminate artifacts when it sums can still be used for making pulses.For example, signal 846A is characterized by a coincident portion 846Fresulting from the gate 841A splitting the applied pulse 839 into twocopies 843 and 844 (FIG. 15H) that are coincident only for the durationof Δt_(Z), thereby determining the width of the coincident portion 846Fof the resulting signal 846A. A non-zero artifact portion 846G resultsat the output of gate 841A where the two copies 843 and 844 do notoverlap. As indicated in the previous discussion, gate 841A may addcoherently or non-coherently depending on its structure and the natureof the light energy in the incident pulse 839. Thus, the ratio of theheight of the pulse portion 846F to that of the non-zero artifact 846Gcan be up to 4:1 or up to 2:1. If coherent summing is done by gate 841A,as also discussed, the artifact may be reduced to one ninth theamplitude of the coincident portion 846F by a circuit 849, that mayrepresent the device of FIG. 13G, that sums with a signal from a CWlaser with the result illustrated 846B, where the zero level isindicated at 846C. The profiles 846A and 846B represent E-fieldprofiles. The power profiles corresponding to signals 846A and 846B areillustrated at 846H and 846K, respectively, with the zero power levelindicated at 846L. Similar results in which the power ratio between thecoincidence pulses and the artifacts is enhanced to be 9:1 can beachieved when using input pulses with non zero background level. Thisratio can even further be increased by complete elimination of theartifact pulses using the optical embodiments illustrated by FIGS.12A–12K. Alternatively, an electronic threshold device may be used in anend unit that receives the optical signal from gate 841A and, in anycase, converts the optical signal it into electronic signal whether anoptical threshold mechanism is used or not.

Note that a configuration like that of FIG. 15F or 15G may be used togroom pulses of any optical modulation scheme. For example, rather thanregenerate pulses in long haul optical links, pulses may be “chopped” orreshaped using such a configuration with suitable optical amplificationto regenerate the power level.

Referring to FIG. 15J, to use such a mechanism in a multiplexer 3840,broad pulses from a laser 843A modulated by a modulator 843B to producerelatively wide pulses 843C at laser output 843D, that are distributedto multiple channels 3847 (typ.) each supplied with a respective gate3845 (typ.) as described with reference to FIGS. 15F and 15I. Eachchannel also has a respective time delay as indicated at 3805 (typ.).Modulators 3806 (typ.) on each channel 3847 (typ.) determine whether apulse is passed on that channel or not in response to a control signalfrom a respective data source 3801 (typ.). A respective symbol isapplied to the signal on each channel 3847 (typ.) by a respectivesymbolizer 3818A (typ.). As in the embodiment of FIG. 15C, the resultingoutput at 3809 illustrated by signal 843F may be in the form of a highlydense series of pulses constructed by very dense symbol signals havingzero level 584A. Again, a synchronization recovery circuit may beprovided and may be integrated in modulator 843B, to ensure thatmodulators 3806 (typ.) are controlled such that the signals from datasources 3801 (typ.) are properly synchronized with the output 843D ofthe modulated laser 843A. For example, a synchronization signal 3811 maybe generated by a detector in 843B that receives a small portion of thesignal that laser 843A emits (not shown separately).

Optionally, to provide a non-zero background which when coherentlysummed as discussed with regard to FIGS. 10D and 11B, a low-level CWsignal 580 may be added to the signal 843F by means of a summer 592 andguide 580B.

The CW signal 580 may be derived from the same source as modulated laser843A which may be configured to provide one output that is notmodulated, as illustrated in FIG. 15L. That is, a CW laser 586(corresponding to 843A of FIG. 15J) may output to a junction 589providing a constant signal 580A corresponding to CW signal 580 of FIG.15J. The other leg of the junction 589 may be applied to a modulator 587(corresponding to 843B of FIG. 15J), such as an LCD or Mach ZhehnderInterferometer (MZI) modulator with a modulation signal supplied by aclock 590 to produce a regular pulse stream 588 corresponding to output843D of laser 843A of FIG. 15J as discussed above. Assuming appropriatecontrol of phase and signal level, the output 843F with a background atzero level 584A is converted by summing in summer 592 to a signal 843Ewith a non-zero floor, as indicated by the zero level 585, to enhancethe intensity ratio between the coincidence signals and the artifactsignals that might exist in the demultiplexing system (not shown) and aspreviously illustrated by FIG. 10C. The enhancement system that includessummer 592 and CW signal 580 may not be needed when coincidence gates3845 (typ.) are of the type of gates 101 that include optical thresholdas shown by FIGS. 12A–12K.

In an alternative embodiment, the same role as signal 580 may be playedby a laser 595 that is separate from laser 843A as indicated. In such acase the phase matching between laser 595 and the signal 843F may becontrolled by a control mechanism for recovering the phase. For example,a detector 593 detects a portion of the power of the signal 843E tapedinto detector 593 and generates a feedback control input to a controller591 that controls a phase shift by variable phase shifter 594 tomaximize the signal power detected. Such a mechanism performs a functionof Phase Locked Loop (PLL). As this is an alternative role for signal580, it is marked in dashed lines and can be used instead of signal 580and guide 580B.

Note that in the discussion of figurative illustration of signals, suchas 843F and 843E, the same diagram may connote the field or theintensity, which is the square of the field. This should be clear fromthe context and no contradiction is implied. Thus, in indicating a shiftin zero level from signal 584A to signal 585, signal 843F and 843E maybe interpreted to represent the field level, but ignoring the zero levelindication, they may be interpreted to represent intensity. Note thatFIG. 15J may be interpreted to be consistent with the use of a multimodelaser within modulated laser 843A. In that case, of course, the non-zerobackground device 580B, 592, etc. would not be applicable.

Instead of providing a separate gate 3845 (typ.) on each channel 3847(typ.), a single gate may be located immediately following the singleoutput 843D of the modulated laser 843A to produce narrow pulses thatare distributed to all the channels 3847 (typ.)

FIG. 15K illustrates the foregoing multiplexer/demultiplexercombinations and others as a generic schematic. A signal vector source832, which may consist of any number of signals (having controlledamplitudes and phases) applied by an input channel 833A to modulators ofeach of multiple parallel channels of a multiplexer 830 outputting ontoa multiplexed channel 836. The multiplexed channel 836 appliesmultiplexed signals to a demultiplexer 834 which applies an outputvector to a receiver 838 via an output channel 833B. Multiplexer 830 mayrepresent multiplexers, such as, the multiplexers of FIGS. 15C and 15J.Demultiplexer 834 may represent demultiplexers, such as, thedemultiplexers of FIGS. 14A–14D and 15E.

Referring now also to FIGS. 15K and 15M, although the input channel 833Aand output channel 833B of FIG. 15K are shown as a single line, itshould be understood that they may have many different componentsrepresenting different subchannels. For example, each component of thesignal vector source 832 may represent a data stream from a separatesources of data such as independent devices S_(n) and S_(m) (amongothers not shown) sending data to specific independent devices S_(p) andS_(q) (among others not shown), as illustrated in FIG. 15M.

As another example illustrated in FIG. 15N, the signal vector source832C may be a parallelized signal from a single source spatiallymultiplexed by a spatial multiplexer 830A (which may be operable in adifferent medium from that of the multiplexer 830). At the receivingend, the separate channels from the demultiplexer 834 may be multiplexedby a different multiplexer 834A and applied to a receiver 838C.

Referring to FIG. 15P, the pulse-pair symbology discussed with referenceto the foregoing embodiments may be used for self control of informationflow by multiple layers of gates. For example, when a signal 862, whichis the multiplexed signal of separate sources of data such asindependent devices S_(a) and S_(b), passes through a demultiplexer 864using multiple gates such as gate 101, energy is output along a chosenone of multiple paths (e.g., 870, 872), each leading to differentdestinations which may include additional demultiplexers (e.g., 868,866). From multiple demultiplexers 866 and 868 the demultiplexed signalsare received by multiple receivers S_(x) and S_(y). The details of thesymbology for multiple layers of demultiplexing are discussed below.Note that the demultiplexers in the embodiments of FIGS. 15K–15N mayrepresent demultiplexers for multiple layers, as, the type illustratedby FIG. 15P.

Referring now to FIGS. 15Q and 15R, it should be noted that thestructure of the gate-based demultiplexer of FIG. 15E can be used inembodiments other than where access is controlled to a common channel bytime division. A more generic embodiment is an array of gates form ademultiplexer as shown in FIG. 15Q where a common signal 895 at input895A generated by some source and encoded with symbols is distributed bydistributor 895B and is passed by a unique gate 890A–890C. For example,such a demultiplexer 893 (FIG. 15R) may be used in a system where theability of multiple senders 891A–891C to transmit through many-to-onecombiner 891D on a common channel 897 is regulated by controller 896.More specifically, contention is resolved by requesting access to thechannel from the controller. Each sender 891A, 891B or 891C encodessignals according to the ultimate destination (not shown) and transmitsonly when the common channel is free. In this configuration various datastructures can be sent including information packets. The latter isdetermined by controller 896 which grants permission to the senders891A–891C. There is no need for self demultiplexer 893 to have anycontrols or even suffer a configuration data, as it may direct the datapassively. Thus, the controller and its arbitration function can belocated at the location of the senders or any other location that isconvenient.

Referring to FIG. 15S, an m-by-n cross-connection configuration has msenders 884A, 884B, 884C connected to respective demultiplexers 882A,882B, 882C. The present configuration allows each of the m senders 884A,884B, 884C to be granted access to a given one of n channels, 887A,887B, 887C, each connected to a respective output channel. Arbitrationmay be performed by controller such as schematically illustrated bycontroller 889, which grants requests for access to a given channel887A, 887B, 887C if the channel is free. The signals are encoded, bysymbols, for a respective one of n receivers 886A, 886B, 886C anddirected to the same by each demultiplexer 882A, 882B, 882C. Contentionarises because signals are summed by star couplers 888A, 888B, 888C sothat each receiver 886A, 886B, 886C can receive from all senders 884A,884B, 884C. But in this case, the senders 884A, 884B, 884C contend foraccess to a given receiver, but can still send to other receivers 886A,886B, 886C when they are free. Also other senders 884A, 884B, 884C cansend to other receivers 886A, 886B, 886C as permitted and determined bycontroller 889. This assumes that each sender 884A, 884B, 884C has theability to articulate optical signals according to a protocolappropriately handled by the gates (not shown) within the demultiplexers882A, 882B, 882C. But, again, arbitration can occur conveniently at thelocation of the senders because no configuration is required at thecross-connect (the demultiplexers 882A, 882B, 882C). This may providespeed advantages in some applications, since unlike the TDM, in whichonly one channel can be inserted at each time slot, the configuration ofFIG. 15S allows the insertion of all the input channels at the same timeto any and each time slot.

Referring now also to FIG. 15T an alternative structure 899J to thebranching structure 883 of FIG. 15S, which employed star couplers 888A,888B, 888C may also be configured using reverse Y-junctions 899G (typ.)that combines multiple ports 899A–899D into a single port 899E.Alternatively a combination of the above structures may be employed witha similar effect, for example where many channels are combined.

Referring now to FIGS. 16A, 16B and 16C the pulse-pair symbologydiscussed above may be applied in multiple layers of parallel gates 101.To accomplish this, symbol 902 including pulse pair 902B encoding adestination is formed, by duplication of pulse 902A, using symbolizer901, just as with the duplication of a single pulse (e.g., 819 of FIG.15B), as discussed with reference to FIGS. 15A and 15B. The timeseparation between the pulses of pair pulses 902B is equal to the timedelay Δt₃ of symbolizer 901. Signal 902 of FIG. 16B is duplicated in asimilar way, by symbolizer 904, to produce symbol 906 containing copies906A and 906B of pair pulses 902B. Pair of pulses 906A and 906B ofsymbol 906 are separated by time space that is equal to the time delayΔt₂ of symbolizer 904. Time delay Δt₂ corresponds to the delay of anadditional gate in an additional demultiplexing/switching layer (notshown) through which signal 906 may be passed before it reaches a gate(also not shown) with a time delay of the respective pulse pair 902B(Δt₃). The process may continue to repeat itself as needed and shown inFIG. 16C yet another layer of symbology may be added by means of anothersymbolizer 910. Here, each set of pulses making up each symbol in signal912 is reproduced at an appropriate interval spacing by anotherduplicator circuit 910 configured with a delay of Δt₁. Symbol 912includes pairs of pulses 912A–912D produced by symbolizer 910 thatcopies double pairs 906A and 906B of symbol 906 to produce copies ofdouble pairs 912A and 912B and double pairs 912C and 912D separated bytime space Δt₁, equals to the time delay of symbolizer 910. The encodingfor the demultiplexing/switching for the three layers represented by theintervals Δt₁–Δt₃ can be processed in any desired order.

Referring now to FIG. 16C, illustrating symbol 912 (typ.). Signal 912includes sets of subgroups of pulses separated by time delays Δt₁–Δt₃,each of these delays represents the encoding for differentdemultiplexing/switching layer. Each set of signals 912 (typ.)represents a single symbol from an original source signal encoded bysymbolizers 901, 904 and 910 of FIGS. 16A, 16B and 16C, respectively.Each of the time intervals Δt₁, Δt₂, and Δt₃, selects a uniquecoincidence gate switch in a given layer of gate systems. Each output ofa gate, such as gate 101 (typ.), in a first layer, corresponds to adifferent and unique value of Δt₁ (typ.). Each output of a gate in asecond layer, corresponds to a different and unique value of Δt₂ (typ.).Each output of a switch in a third layer, corresponds to a different andunique value of and Δt₃ (typ.). The encoding order illustrated by FIGS.16A, 16B and 16C is only one example of many other possible encodingorders. In general, the encoding order is arbitrary and may be chosen asdesired.

Signals 912 (typ.) may represent encoded symbol for any number of layersand may be at any desired length. However for maintainingsynchronization a specific fixed time frame may be defined capable ofincluding the longest symbol 912 (typ.). Any time frame produces onlyone coincidence signal by the specific gate 101 (typ.) at the lastdemultiplexing/switching layer designed to respond to specific symbol912 that the specific frame includes. Thus in order to maintainsynchronization where the propagation of the signals is from left toright, each symbol 912 should start on the left edge of each time frame.

A guard interval between the time frame of symbols 912 (typ.) maintainsa distance between adjacent time frames may be any width sufficient toprevent inter-symbol interference, for example, the maximum time delayused for a previous symbol. In case that the artifact pulses arecancelled, the guard zone requirement may only exist at the layer withthe highest encoding delay. This is because the time delays thatcorrespond to the other layers are always a fraction of the delay atthis layer, the presence of the highest guard interval guarantees thatno overlap will occur between successive symbols in the lower layers.

Note that, generally, in the foregoing illustrations, artifact pulsesmay be left out of signals, even though it may be present in certainembodiments, depending on the nature of the embodiment used for form thepulse-pair symbols.

Refer now to FIG. 16D, which illustrates further how the multilayersignal is processed through multiple layers gates (without showingartifact pulses to simplify the figures, although they may or may not bepresent). The original signal (e.g. 912 from FIG. 16D) here shown at940, is applied to a first layer 946 of gates 952A–952F each with arespective time delay Δt_(a)–Δt_(f) (illustrating specifically, forexample, Δt₁ that matches gate 952C). Gate 952C, which is within therange of gates 952A–952F (a range which has an arbitrary number of gateswithin the confines of the encoding range), outputs coincidence signal930 because it is configured for the matching time interval Δt₁. Signal930 may be thought of as containing the structure of one half of thesignal 940 and results due to the coincidence effect described forcoincidence gates above. The other gates in the layer 946 output nosignal, because their time delays have non-matching values.

Signal 930 is applied to the second layer of gates 952N–952R, each witha respective time delay Δt_(n)–Δt_(r) (illustrating specifically, forexample, Δt₂ that matches gate 952P). Gate 952P, which is within therange of gates 952N–952R (a range which also has an arbitrary number ofgates within the confines of the encoding range), outputs signal 932because it is configured for the matching time interval Δt₂. Signal 932may be thought of as containing the structure of one half of the signal930 and results due to the coincidence effect described for coincidencegates above. The other gates in the layer 948 output no signal, becausetheir time delays have non-matching values.

Signal 932 is applied to the third layer of gates 952V–952Z, each with arespective time delay Δt_(v)–Δt_(z) (illustrating specifically, forexample, Δt₃ that matches gate 952X). Gate 952X, which is within therange of gates 952V–952Z (a range which also has an arbitrary number ofgates within the confines of the encoding range), outputs signal 934,because it is configured for the matching time interval Δt₃. Signal 934may be thought of as containing the structure of one half of the signal932 (or a single pulse) and results due to the coincidence effectdescribed for coincidence gates above. The other gates in the layer 950output no signal, because their time delays have non-matching values.Note that in FIG. 16D, the shapes of the pulse patterns are notnecessarily to scale. The decoding order along the multiple decodinglayers, illustrated by FIG. 16D, is only one example of many otherpossible decoding orders. In general, the decoding order is arbitraryand may be chosen as desired. This means that the decoding layers havingthe respective time delays Δt_(n)–t_(r) may be switched in their ordersas needed.

It also should be clear that the self decoding/demultiplexing/switchingsystems discussed above, such as the systems of FIGS. 14A–14D, 15P and16D, designed for self routing of information across multiple switchinglayers may have different configurations. For example, in embodimentswhere coincidence gates used in the self routing system are of the type101 designed for cancellation of artifact pulses (non-coincidencepulses) by exemplary means of optical threshold mechanism, thecoincidence gates should be distributed along the nodes located at therouting layers. However, where the coincidence gates used in the selfrouting system are of the type 101 that allows artifact pulses(non-coincidence pulses) which do not include an optical thresholdmechanism, the same signal may arrive to all of the ports at the lastdemultiplexing/switching/routing layer. Accordingly, such coincidencegates may be arranged to be located only at the terminals of the lastswitching layer. In such a case the switching layers 946, 948, 950 ofFIG. 16D may all be located at the output ports of the system. Still,the configuration described above for gates that do not allow artifactpulses in which the gates are distributed along the nodes located at therouting layers, is usable for gates that allow artifact pulses as well.

In addition it should be noted that the system of FIG. 16D may representa situation where all layers 946, 948 950 are at close vicinity to eachother and at the same radiation guide. In such a case, the system ofFIG. 16D may represent a configuration of several coincidence gatesconnected together in series to form a new combined coincidence gate.Such a gate, responses to form main coincidence pulse (as discussedbelow), only for a specific pattern of a symbol constructed frommultiple pulses with a number of pulses greater than two. The specificaddress (predetermined destination) to which only one specific combinedcoincidence gate responds, is encoded by the specific time spacesbetween the multiple pulses forming the specific pattern of a specificsymbol.

The main coincidence signal is the coincidence pulse with the highestintensity that exists in the system for a specific symbol. While someother coincidence signals may be produced in the same gate where themain coincidence signal is produced or in other gates, still the maincoincidence pulse is the pulse with the highest intensity produced inthe system. A main coincidence pulse only outputs at a specific gatethat matches the time delays between the pulses of a specific address ofa specific symbol.

Note that each gate in the series of gates forming the combinedcoincidence gate of FIG. 16D may be a combined coincidence gate byitself, such as, the combined coincidence gate formed by multiplecoincidence gates connected in parallel and illustrated by the combinedcoincidence gate of FIG. 22A. Accordingly, a combined coincidence gatemay be constructed from coincidence gates connected in series, inparallel or in any combination of serial and parallel connections.

Referring now to FIGS. 16E, 16F and 16G, comparators (differentialamplifiers) 990 may be used at the outputs of a multiple layerarrangement of demultiplexers as described with reference to FIG. 15P(three layers) and as indicated with reference to FIG. 16E. First, asignal may be formed as indicated at 980 of FIG. 16G by a suitablemodulation scheme such as interleaving several layers as discussed withreference to FIGS. 16A–16C. Then in a first layer of demultiplexing asindicated at layer 946 in FIG. 16D, a delayed image 981 of FIG. 16G ofthe signal 980 is summed with the signal 980 with the result at thecoincidence output as indicated at 982. Then in a second layer ofdemultiplexing as indicated at layer 948 in FIG. 16D, a delayed image983 of the signal 982 is summed with the signal 982 with the result atthe coincidence output as indicated at 984 of FIG. 16G. Finally, in athird layer of demultiplexing as indicated at layer 950 in FIG. 16D, adelayed image 985 of the signal 984 is summed with the signal 984 withthe result at the coincidence output as indicated at 986 of FIG. 16G.The above profiles 982–986 are assumed to be representative of power,not field strength. The final result at the non-coincidence output isshown at 987. If these two signals are applied to respective comparator990 inputs 990A and 990B, with respective detectors 993A and 993B, as inFIG. 16E, the result at the output 990C will be as indicated at 988 ofFIG. 16G. The remaining pulses are those that coincided at the finalgate (not shown in the present drawing) with all other artifact beingeliminated. Note that the spacing between the remaining pulses includingthe main coincidence pulse 988A (a pulse that have coincidence in allthe layers) and artifact pulses 988C is increased by the elimination ofthe interstitial pulses coinciding with profile 987. The increase of thespace between the pulses has the advantage of allowing the use of slowerdetectors. The discrimination of main coincidence pulse 988A from theartifact pulses 988C (secondary coincidence pulses that do not havecoincidence in all the layers) is performing by setting an optical orelectronic threshold level 988B which is adjusted to be in the rangebetween the amplitudes of pulses 988A and 988C. Such threshold leveleliminates all the artifact pulses 988C and allows only the propagationof main coincidence pulse 988A.

It should be understood that when the device of FIG. 16E includingcomparator (differential amplifier) 990 is employed in a way describedabove but, after the first demultiplexing layer, only the coincidencepulse appears at output 990C of comparator 990. In such a case there isno need for additional threshold mechanism.

FIG. 17 illustrates how Wavelength Division Multiplexing (WDM) may becombined with the symbology method of the present invention in acommunications system. Multiple instances of theinterleaving/multiplexing system described with reference to FIGS. 15Athrough 15S may be provided, for example as schematically indicated at960 (typ.). Each of the multiplexed channels may be assigned a frequencychannel and multiplexed in a WDM process schematically illustrated by970 for transmission on a long haul channel 965. Correspondingdemultiplexing provided by a WDM demux engine 975 is provided at areceiving end, the respective frequency channels of which may be appliedto respective optical demultiplexers 976 (typ.) and 977 (typ), such asthose illustrated in FIGS. 15A–15S. The label CDM of switches 976 (typ.)and 977 (typ.) stands for Code Division Multiplexing/Demultiplexingreferring to the self routing preformed by the code of the predetermineddestination encoded in the symbols constructed at multiplexing systems960 (typ.) Note that two layers of demultiplexers are shown. These mayemploy the mechanism for multiple-layer encoding described with respectto FIGS. 16A–16D.

Referring now to FIG. 18A, elements of a receiver device for convertingoptical signals output by gates 101 and systems employing them in theirvarious embodiments, are illustrated by a demultiplexing receiver 1000.The demultiplexing receiver 1000 has various features, illustratedfiguratively, that indicate how such a device may be fabricated on anoptical chip using lithographic techniques that may be known in thefield as Planar Circuits (PLC). A signal received on channel 1018 isdistributed by a star coupler 1019 to several gates 1007A–1007C. Eachgate has a respective directional coupler 1002A–1002C, delay line1004A–1004C, and directional coupler 1005A–1005C acting as combiners.Directional couplers 1002A–1002C divide the incoming signal into pathswith different delays and couplers 1005A–1005C sum them, and apply thesummed signal to a optical detector 1006A–1006C.

Each gate 1007A–1007C has a respective phase shifter 1010A–1010C thatadjusts the phase so that coincidence pulses result from constructiveinterference, at couplers 1005A–1005C, provide the maximum ratio ofpulse height to background (including non coincidence pulses).

When device 1000 is made from optical fibers, the phase shifters1010A–1010C can be of the type that applies pressure, by use of apiezoelectric crystal. For device 1000 that is made using planarwaveguides, the phase shifters 1010A–1010C can be of the type thatthermally changes the refractive index of the waveguide, orsemiconductor material fabricated by thin film techniques that changeits refractive index due to injection of charge carriers into itsguiding media. The change in the refractive index shifts the phase ofthe radiation propagating in the media of the shifters 1010A–1010C.

Phase matching can be obtained by use of a suitable calibration byclosed-loop phase controller 1012. A calibration signal may be obtainedfrom any of the signal paths, for example, by means of a detector 1016that taps a small portion of signal energy from directional coupler1005B. The detector 1016 and phase controller 1012 combination mayprovide an instantaneous or averaged signal and be configured tomaximize intensity. Since most properties that affect the phases of thesignals within a small embodiment of receiver 1000 are uniform, forexample if formed on a chip, a change in properties that affects onsignal path should affect all in the same way. Thus, the entireconfiguration of receiver 1000 may be calibrated such that only onedetector is required to provide for control of all the phase shifters1010A–1010C. Temperature changes, for example, in various opticalcomponents may drift, requiring the correction of the phase match. Butthis correction need only be done at long intervals relative to the rateof data throughput through such devices and therefore does not present asignificant obstacle. Suitable control systems for performingcalibration are well within the state of the art and can be embodied inmany different forms.

Although in the embodiment of FIG. 18A, a single input (from detector1016) is used to control multiple phase shifters 1010A–1010C, it alsopossible to control each phase shifter with a separate detector (notshown) for each signal path. In this alternative embodiment (not shown),separate detectors such as 1016 and separate phase controllers such as1012 are used to control each shifter 1010A–1010C. Note also that thephase shifters 1010A–1010C may be provided with the ability to shiftover multiple wavelengths so that they can align pulses. While thepulses are illustrated in the instant specification as square-edged, itis certainly possible and very likely, that real-world pulses would haveround edges and in fact be substantially bell-shaped. The strength of acoincidence pulse, as a result, would be expected to be very sensitiveto the alignment between the two gate inputs. Thus, the phase shifters1010A–1010C may be time-delay shifters with enough latitude that theycan align pulses that are time–shifted more than a fractional wavelengthfrom optimal. The procedure would be the same in either case: search forthe average power intensity peak, which naturally gives greater weightto coincidence pulses.

Threshold inputs 1008A–1008C to respective comparators 1011A–1011Cdiscriminate coincidence pulses from artifact and background byestablishing a minimum signal level output from detectors 1006A–1006C.As a result, the comparators 1011A–1011C output pulses 1021A–1021C onlywhen a coincidence pulse is received by them. The threshold inputs1008A–1008C may be established by various methods. In one embodiment, ahandshake from each sender occurs at regular intervals and a testmessage with a certain number of coincidence pulses and model artifactis sent many times while the threshold level is ramped up and down. Thensome midpoint (or another point in the range between the intensities ofthe coincidence and artifact pulses) may be established in response tothe test exchange and then the threshold level may be fixed thereafterin response.

It should be understood that the optical sensors and the electronicthresholds (comparators) components may be an integral part of thedemultiplexing device, they may be placed in close vicinity to thedemultiplexing device, they may be placed far away from thedemultiplexing device, and even may be placed in an end unit. The sameis true in the situation that optical thresholds are used to replace thecombination of optical sensors and electronic threshold components. Suchoptical thresholds may be an integral part of the demultiplexing device,they may be placed in close vicinity to the demultiplexing device, theymay be placed far away from the demultiplexing device, and even may beplaced in an end unit.

Note that device 1000 may be fabricated from Multi Mode (MM) radiationguides, such as fibers or waveguides. In such a case the radiation incombiners 1005A–1005C is summed incoherently and there is no need forthe phase control. Accordingly, when MM radiation guides are used indevice 1000, detectors 1006A–1006C, controller 1012 and shifters1010A–1010C may be removed resulting in a simpler device. Though MMdevice 1000 has the advantage of simplicity, it has a disadvantage oflower contrast between coincidence and artifact pulses.

Referring to FIG. 18B, an example of applying the comparator(differential amplifier) embodiment of FIGS. 16E and 16F is shown. Eachor any of gates 1007A–1007C of FIG. 18A (exemplified by gate 1009E inFIG. 18B) may apply their respective coincidence and non-coincidenceoutputs 1009A and 1009B to respective detectors (not separately shown,but housed in detector device 1009C. The corresponding signals may thenbe differentially applied to a comparator 1009D to eliminate theartifact pulses.

Fabrication of delay lines on a chip presents some problems because ofthe minimum radius of turns required to ensure tolerable band loss inthe turns. The required radii and the requirement to avoidcross-intersection between the radiation guides may cause the amount ofreal estate required for large delays to be too great for practicalmanufacture and even if they can be manufactured, the waste of realestate would make such a configuration uneconomic. A configuration thatis much more susceptible to convenient lithographic fabrication on achip is shown in FIGS. 19, 20A and 20B

Referring to FIG. 19, here a series of directional couplers 1028, 1032,1034, 1036 fabricated on a chip 1030 and associated with radiationguides 1025A–1025E directs a signal 1026 from an input port 1024 to anoutput port 1038 to form an optical delay line 1020. Edge surfaces aremirrored by cleaving, polishing, or coating and each directional coupler1028, 1032, 1034 and 1036 has a coupling length that is equal to half ofthe length required for crossover. In such a case the radiation thatenters to any coupler 1028, 1032, 1034, 1036 is distributed along thecoupling region of the coupler and is reflected back, from mirror likeedges 1040 (typ.), along the same coupling region. Accordingly, the backand forth propagation of the radiation in the coupling region of eachcoupler 1028, 1032, 1034, 1036 is along a distance that is equal to acoupling distance of a complete crossover. This means that when theradiation enters to couplers 1028, 1032, 1034, 1036 from one port it iscompletely reflected back from the other port. Thus the light isreflected back and forth along the directional couplers 1028, 1032,1034, 1036 and light guides 1025A–1025E to create an optical pathbetween input 1026 and output 1038 with little backward reflection.

Referring to FIG. 20A, in a variation on the above, the directionalcouplers 1028, 1032, 1034, 1036, typified by 1044, employBragg-reflector gratings 1046 (typ.) instead of a reflective mirrorsurface 1040 (typ.) of FIG. 19. The coupling length for completereflection is achieved by the provision of a directional coupler whosecoupling length (measured from the point where total reflection isproduced by the Bragg grating) is half of that required for crossover.

In another variation shown in FIG. 20B, the Bragg gratings 1046A and1046B are provided beyond the coupling regions 1044A (typ.) of thedirectional couplers 1044B (typ.). The locations of the gratings shouldbe equidistant from the coupling regions 1044A (typ.) so thatback-reflection losses are minimal and this may require slightlydifferent offsets for the Bragg grating as indicated in the drawing.

It should be noted that in the configurations shown in FIGS. 19, 20A and20B, there is no use of large radius bends along the path of the delaylines, resulting in delay lines with a very compact structure with smalldimensions across the traverses. Accordingly, such configurations fordelay lines are very attractive for on-chip fabrication.

Referring now to FIG. 20C, in an implementation of the delay embodimentsof FIGS. 19, 20A and 20B, a gate 1031A has single mode directionalcouplers 1023A and 1027A which split a signal entering coupler 1023Ainto radiation guides 1035A and 1037A and create a sum signal in coupler1027A. Preferably the coupler 1023A is such that more than 50% of thesignal power is sent into the delay branch 1021A, to compensate forpossible loss in the delay branch 1021A, such that the delayed andnon-delayed signals arriving from guides 1035A and 1037A, respectively,summed in coupler 1027A are substantially equal in power. A phasecontroller 1025A is provided to ensure phase alignment of the delayedand non-delayed branches is correct for maximizing the differencebetween coincidence and non-coincidence pulses.

Referring now to FIG. 20D, illustrating an embodiment 1021B that is avariation of the design of embodiment 1021A of FIG. 20C. Embodiment1021B avoids the need for a phase controller 1025A by employing amultimode coupler 1027B, which has tapered branches 1027C and 1027D thatallow adiabatic transmission from single mode radiation guides 1035B and1027B to multimode coupler 1027B with reduced loss. Coupler 1027Bperforms power-summing rather than field-summing. In this case, becausethe summing is non-coherent (as opposed to the use of a single modedirectional coupler 1027A of FIG. 20C) there is no need for phasealignment. In this configuration, the segment of the delay line 1021B ismade of single mode radiation guides, in whom the coupling length ofcouplers 1021B is well defined, but the summing coupler 1027B is amultimode (MM) coupler that may avoid the need to use phase shifter1025A. Coupler 1023B may be similar to coupler 1023A of FIG. 20C.

Referring now to FIG. 20E, a compact structure for delay linesfabricated on chips that lacks any intersections between its radiationguides 1050 and 1051 including their input and output 1052 and 1053 isillustrated. The delay line is configured by a core of open loop 1050around which the pair of radiation guides 1051 and 1052 are loopedtogether. The structure has an initial radius R₀ and pitch between theguides of D. Each turn of the guides adds D to the total radius of thebend and 2*D to the width W of the group of delay lines. The total widthof the delay lines for N turns is 2*(R₀+N*D). For example, aconventional delay line (constructed from an optical guide that isrouted back and forth with a turning region of some minimum radius) withthe same length and R₀ would have a width of 2*N*R₀. Since D<<R₀, thewidth of the delay line shown in FIG. 20E is much smaller than that ofanother delay line, having the same delay, and fabricated conventionallyon a chip. The delay line of FIG. 20E may be useful for on chipfabrication and may be used in the devices of FIGS. 20C and 20D, toreplace respective delay lines 1021A and 1021B.

Referring now to FIGS. 21A, 21B and 21C, various mechanisms formodulating and demodulating are shown. In FIG. 21A, a firstmodulation/demodulation mechanism that is similar to the embodiment ofFIG. 15C. Here a pulse source P distributes pulses using a distributiondevice 1065A, for example a star coupler, a cascade of directionalcouplers, a cascade of Y-junctions, or a cascade of other splitters, tomultiple modulators as shown at 1068 (typ.). Each modulator 1068 feedsinto a respective time delay 1069 (typ., but with different delaysΔt_(X)−nΔt_(X)) and duplicator 1067 (typ., but with different delaysΔt_(Z)−nΔt_(Z)). The delays space apart the signals generated by themodulators 1068 so that the symbols generated by duplicators(symbolizers) 1067 (typ.) are interleaved, without collisions, intocombiner 1065B that merges them onto a common data path 1058D. Formaintaining synchronization, the interleaved symbols at common data path1058D may be interleaved into fixed size of time frames where each ofthe symbols may start at the delayed edge of each time frame.

For demodulating, the symbols from common data path 1058D aredistributed, by device 1058A, into an array of gates 1058B–1058C (typ.but with different delays Δt_(Z)−nΔt_(Z)) and are demultiplexed by thisarray of gates in a manner similar to earlier embodiments.

Referring to FIG. 21B, data may be directly modulated onto a singlechannel 1075A using a modulator 1070 under control of a clock 1073 andaddress (predetermined destination) and data sources 1071 and 1072 toform symbols, at channel 1075A, as previously discussed. The symbolstream on channel 1075A may be split among multiple channels, asdiscussed in prior embodiments, using a demodulator 1079D and sent torespective destinations 1079B–1079D that may include receivers R₁–Rn.

Referring to FIG. 21C, illustrating a system similar to the system ofFIG. 211B with an additional sequence manager. In the alternativeembodiment of FIG. 21 C, a sequence manager 1078 receives address datafrom address (predetermined destination) source 1071 and a clock signalfrom clock 1073. The sequence manager 1078, which may be implemented asa programmable processor or preferably a simple state machine such as anASIC (application specific integrated circuit), generates a pulse,through electrical lead 1078A, that is used to control modulator 1070.The sequence manger 1078 controls when the next symbol should be output,at channel 1076D, by the modulator 1070 responsively to address source1071. The symbols generated at guide 1076D, by modulator 1070, aredemultiplexed, as discussed above, by demultiplexer 1079D having outputterminals 1079B–1079D that may include receivers R,-R,. The reason formaking the symbol rate responsive to the address is to minimize thedelay between symbols required to avoid inter-symbol interference, asexplained with reference to FIG. 21E, as described below.

Referring now to FIG. 21D, multiple modulators 1084A–1084C governed by acommon clock 1083 and transmitting for multiple respective addresses1081A–1081C and data 1082A–1082C may be governed by a common sequencemanager 1080. The output signals from each modulator 1084A–1084C,propagating on channels 1086A–1086C, may be interleaved by a combiner1088, onto a single channel 1087. In this case, the sequence manager1080 also manages for collision avoidance, since multiple independentdata streams from channels 1086A–1086C may vie for the same channelsspace at common channel 1087.

Referring now to FIG. 21K, highly dense pulse streams can be generatedusing electronic modulation not only to determine whether a coincidencepulse will be generated at a final destination as in foregoingembodiments, but also to actually determine the particular symbol (e.g.,spaced pulse) as well. In other words, the system may perform the symbolmodulation electronically.

First a stream of narrow pulses generated by means of any of theforegoing mechanisms is generated on each of a number of parallelchannels 1228A–1228P. The spacing of the pulses (e.g., 1224B typ.) oneach channel (e.g. 1228A typ.) may be equal to the size of the timeslots multiplied by the number of channels and synchronized across allthe channels 1228A–1228P such that every time slot has a single pulse inone of the channels according to a repeatable scheme. Modulators A–P1122 (typ.) control whether pulses on respective channels 1228A–1228Pare passed to a signal combiner 1226 to be emitted from port 1227. Ifall the pulses were passed by all the modulators A–P 1222 (typ.), theresulting train of pulses would be equally spaced pulses a single timeslot apart. The modulators A–P 1222 (typ.) are all controlled by acontroller 1230 to form spaced-pulse symbols according to a desired datastream (not indicated) on a single output channel 1227. The resultingsignal, illustrated at 1226 may include a series that includes the pulsetiming positions of pulses 1224A, 1224B, 1224C and others, illustratedby pulses 1225A, 1225B, 1225C and others, respectively, with theinter-symbol spacing as well as the selection of the symbol from thesymbol space being determined by the controller and contributed to byall the channels in concert.

It is clear that using the same method, symbols including number ofpulses greater than two, such as symbols 912, 940–944 and 1130–1134 ofFIGS. 16C, 16D and 22A, respectively, can be produced at port 1227.

In another embodiment, a similar system of FIG. 21K, is illustrated atFIG. 21L. Modulators 1244 (typ.), combiner 1240, output channel 1241 andcontroller 1238 of FIG. 21L may be the same as indicated by 1222 (typ.),1226, 1227 and 1230 of FIG. 21K, respectively. The data modulated ontothe output channel 1241 may come from a buffer 1236 such as a FIFO todrive the controller 1238 that controls the modulators 1244 (typ.).Buffer 1236 receives multiple parallel channels such as 1234A–1234C. Apulse former 1242 may be present in each channel to reduce the width ofpulses as described with reference to FIGS. 15F or 15G. One or moresources of pulses 1248 may be provided and the pulses distributed toeach channel as discussed with respect to FIGS. 15C and 15J.

Note that although the above figures refer to the address symbols (e.g.,1071 of FIGS. 21B and 21C or 1081A–1081C of FIG. 21D) and data (e.g.1072 of FIGS. 21B and 21C or 1082A–1082C of FIG. 21D) as beingdifferent, it is possible for them to be one and the same. That is, thesymbology may encode data that is sent to a single destination, and itmay represent any data, not just destination data. That is, the data maybe encoded such that each pulse-spacing symbol indicates a datum, forexample, such that the number of bits carried is log₂(N,) where N is thenumber of time slots. By providing a mechanism for generating pulses onselected channels, therefore, messages may be received by associatingeach channel with a particular degree of freedom of a message format.

The delay following each symbol that is required to prevent inter-symbolinterference (called a guard band) may depend on the particular symbolsand decoding gates used in the decoding system. For example, this may bethe case when a pulse-spacing symbology is used with gates that allowartifact pulses as discussed below and shown in FIG. 21E.

FIG. 21E illustrates 5 identical groups 1052A–1052E of encoded symbols.In each group 1052A–1052E there are 5 different encoded symbols. Thespace between the pulses of the shortest symbol is Δt and the spacebetween the pulses of the longest symbol is 5Δt. Groups 1052A–1052E areeach the same, but the effect of passing each through a different gate(indicated at 1061A through 1061E) is illustrated in the regions 1053and 1055. The effect of passing through gates 1061A–1061E, shown inregions 1053 and 1055, is equivalent to summing of the symbols withtheir delayed copies where each of gates 1061A–1061E produces adifferent delay. The shortest delay is of gate 1061A and is equal to Δt.The longest delay is of gate 1061E and is equal to 5Δt. Gates1061A–1061E having time delays Δt, 2Δt, 3Δt, 4Δt and 5Δt, respectively.Region 1053 represents a time frame that is capable of including thelargest symbol used in the decoding system. Region 1055 represents thetime guard band between frames 1053 (typ.) that should be maintained toavoid unwanted inter-symbol interference. It can be seen that all thecoincidence signals produced by gates 1061A–1061E for the symbols ofgroups 1052A–1052E appear in region (time frame) 1053. Region 1055(guard band) includes only artifact pulses. Each shaded rectangle, forexample 1051 (typ.) represents a pulse. Artifact pulses such asindicated at 1056 are indicated as being at half the height ofcoincidence pulses (non-coherent summing), for example, as indicated at1051. As can be seen from the figure, the maximum number of time slotsoccupied by artifact pulses (e.g., 1056) is equal to the maximum delayof the gates 1061A–1061E. This maximum (5δt) is produced by gate 1061Ewith the greatest delay which produces the coincidence pulses andartifact pulses shown at 1059. The minimum inter-symbol guard band isshortest for symbols 1059A having pulses spaced only one time slot apart(Δt) 1057 as indicated in the top row of the last group at 1059B. Thedelay is one time slot spacing longer (Δt) 1057 when the pulse spacingis one time slot longer and so on. The size of the guard band should beat least the size that avoids inter-symbol interference for the longestsymbol 1059E that produces artifact pulse 1059F when passing throughgate 1061E (having delay of 5Δt). Accordingly, the size of guard band1055 is 5Δt which is equivalent to the length of the longest symbol usedin the system.

Referring now to FIG. 21F, three pulse-spacing symbols 1090A–1090C, withrespective guard bands 1093A–1093C (indicated by a dot-filled region)following each symbol, are shown. Each symbol has first and secondpulses, for example symbol 1093A has the pulses 1097A and 1097B. Thepulses 1097A and 1097B are each located in one of eight, for example,allowed time slots indicated at 1098 (typ.). The guard bands 1093A–1093Cmay be fixed in size as shown. Each symbol may be spaced a fixedinterval apart as shown, the interval being the maximum delay betweenspaced pulses plus the maximum length of each symbol. For example, thepulse spacing illustrated for symbol 1090A is the largest permitted witha spacing of seven time slots giving it a symbol length of eight timeslots. The guard band is the maximum delay of each gate, which is seventime slots. The spacing between each symbol is therefore 15 time slots,which is the maximum required to prevent, in any case, artifact pulsefrom a leading symbol from overlapping in a gate with a trailingsymbol's pulses. The fixed symbol spacing may be obtained using any ofthe foregoing modulators in FIGS. 21A–21C or any pulse-spacingmodulators discussed elsewhere in the specification.

Referring now to FIG. 21G, a more efficient spacing of symbols employs avariable delay such as may be provided by modulators 1068 of FIGS. 21A,1070 of FIGS. 21B–21C and 1084A–1084C of FIG. 21D, and sequence managers1078 of FIG. 21C and 1080 of FIG. 21D. Here, the guard band followingeach symbol 1103A–1103D begins immediately after the second pulse ofeach symbol 1100A–1100D and its size is equal to the delay of the gatehaving the longest delay. Since the maximum delay between a pulse andany artifact produced from it is equal to the longest delay of a gate(as can be verified by inspection of FIG. 21E), this arrangement willproduce no inter-symbol interference for a single layer system.

Referring to FIG. 21J, the guard band delay can be eliminated in aseries of time delay symbols 1260 while still preventing inter-symbolinterference in the above embodiments and thereby increase symboldensity. To do this, each pulse (e.g., 1250, 1252, 1256 and so on) maybe employed to define the time delay for a current symbol and as areference pulse for the formation of a following symbol. Morespecifically, let pulse 1250 be a first reference pulse. Then pulse 1252would produce a coincidence pulse in a gate with a time spacing of 1time slot (having a 1 time slot difference between pulses 1250 and1252). The Pulse 1256 would then produce a coincidence pulse in a gatewith a time delay of 4 time slots (having a 4 time slots differencebetween pulses 1252 and 1256) and 1257 a coincidence pulse in a gatewith a time delay of 7 time slots and so on. Delays are indicated indimensional designations as shown at 1253. Each pulse 1250–1256 thusserves a double role in indicating the time delay for a current symboland serving as a reference for a following symbol. Several consecutiveexamples are shown in succession at P01 through P07.

Using such a technique is very useful when multiple symbols are sent tothe same destination. In such a case, a stream of pulses spaced by aspecific time delay corresponding to a specific gate destination may beformed to direct information to this specific gate. In this case, eachpulse serves double duty, as a pulse indicating the delay (time space)of a current symbol (data/control pulse) and as a reference pulse forthe next following symbol (control/data pulse). This configurationallows saving in the number of pulses used to demultiplex informationinto the desired destinations.

The protocol of FIG. 21J can be implemented using a device as describedwith reference to any of the above modulators susceptible to dynamiccontrol.

Referring now to FIGS. 23A, 23B, and 23C, gates, exemplified here by adielectric beam splitter 1310 may provide signal control based on therelative phases of input signals. A signal 1315 at a first port includesa pulse 1325 whose phase is indicated as 0 with a field amplitude of√{square root over (2)}, results in outputs at the ports 1312 and 1313of signals whose field amplitudes are both equal to unity. The phases ofthe outputs at ports 1312 and 1313 are indicated as 0 at 1345 and π/2(j) at 1350, respectively, because these represent the relative phaseshift that occurs due to transmission and reflection by the beamsplitter 1310 as discussed above.

A signal 1360 (FIG. 23B) incident at a second port includes a pulse 1355whose phase is indicated as 3π/2 (−j) with a field amplitude of Hi,results in output pulses 1341 and 1336 at the ports 1312 and 1313,respectively, of signals whose field amplitudes are both equal to unity.The phases of the outputs at ports 1312 and 1313 are indicated as 0 at1365 and 3π/2 (−j) at 1370, respectively, because these represent therelative phase shift that occurs due to transmission and reflection bythe beam splitter 1310 as discussed above.

When pulses 1395 and 1385 of FIG. 23C are incident together withrespective phases 3π/2 and 0, all the energy is output at port 1312 aspulse 1390 whose field amplitude is 2 and whose phase is indicated as 0at 1397. No energy emerges from the second port 1313.

Referring now to FIGS. 23D–23F, showing same gate 1310 of FIGS. 23A–23C,having output ports 1312 and 1313. Analyzing FIG. 23D similarly asdiscussed above with respect of FIG. 23A, if the phase of one of theinput signals, e.g., 1315′, is rotated by π, the similar results obtainfor singly-incident pulses, but the port from which all of the outputenergy emerges when the input pulses are coincident shifts to the otherport as will be observed. That is, a signal 1315′ at the first portincludes a pulse 1325′ whose phase is indicated as π with a fieldamplitude of √{square root over (2)}, results in outputs at the ports1312 and 1313 of signals whose field amplitudes are both equal to unity.The phases of the outputs at ports 1312 and 1313 are indicated as −π at1345′ and 3π/2 at 1350′, respectively, because these represent therelative phase shift that occurs due to transmission and reflection bythe beam splitter 1310 as discussed above.

FIG. 23E is identical to that of FIG. 23B. It is illustrated for thecompleteness of the steps towards the similar analysis of FIG. 23F. Thesituation in FIG. 23F is identical to that in FIG. 23C. When pulses 1385and 1395′ are incident together with respective phases 3π/2 and −π, allthe energy is output at port 1313 as pulse 1390′ whose field amplitudeis 2 and whose phase is indicated as 3π/2 at 1397′. No energy emergesfrom the second port 1312.

As will be observed, by controlling the relative phases of pulses at twoinput ports, the port from which energy is emitted can be controlled.The above effect is used in several switching and gating systems thatare now discussed. An illustration of a means by which the relativephase may be used for a symbology is illustrated in FIGS. 23G and 23H.

It is clear that similar behavior may be achieved with other summingdevices and especially with those illustrated by FIGS. 1A–1D, 2A–2C,3A–3C, 4A–4E, 5A–5C, 6A–6C, 7A–7B and 8A–8E.

Referring now to FIGS. 23G and 23H, a spaced pulse symbol 1404 withfirst and second pulses 1408A and 1408B having a spacing such that whenthe first pulse 1408A is delayed and coherently summed in a gate 1406, acoincidence pulse 1408 is produced at a first output 1406A. The summingprocess that produces the coincidence pulse is illustrated by the vectorrepresentations with 1412A and 1412B representing the undelayed resultof passing signal 1404, and 1414A and 1414B representing the delayedresult of passing signal 1404. The configuration of the gate 1406 issuch that the delayed and undelayed pulses 1412B and 1414A arecoherently summed to produce coincidence signal 1408. At the secondoutput 1406B, the interaction of the delayed and undelayed pulse pairsindicated at 1416A, 1416B and 1418A, 1418B, respectively, produce adestructive interference of pulses 1416B and 1418A and no coincidencepulse emerges from the second output 1406B. Thus, √{square root over(2)}/2 of the field amplitude of the first pulse 1408A is combined with√{square root over (2)}/2 of the field amplitude of second pulse 1408Bso the power in the coincidence pulse 1408 is double the power of eitherthe first or second pulse 1408A, 1408B. The energy at the noncoincidence output 1406B is zero and thus the total energy in the inputsis preserved at the outputs.

Referring in particular to FIG. 23H, the power of a single pulse can bepreserved in a coincidence pulse emerging from the second output 1406Bof the same gate 1406 by providing a phase difference between incomingpulses 1438A and 1438B of π radians from the phase difference of pulses1436A and 1436B (of FIG. 23G). Here, a spaced pulse symbol 1434 withfirst and second pulses 1438A and 1438B having a spacing such that whenthe first pulse 1438A is delayed and coherently summed in the gate 1406,a coincidence pulse 1438 is produced at the second output 1406B. Thesumming process that produces the coincidence pulse 1438 at output 1406Bis illustrated by the vector representations with 1426A and 1426Brepresenting the undelayed result of reflected signal 1434, and 1428Aand 1428B representing the delayed result of passing signal 1434. Theconfiguration of the gate 1406 is such that the delayed and undelayedpulses 1426B and 1428A are coherently summed. At the first output 1406A,the interaction of the delayed and undelayed pulse pairs indicated at1422A, 1422B and 1424A, 1424B, respectively, produce a destructiveinterference of pulses 1422B and 1424A and no coincidence pulse emergesfrom the first output 1406A. Thus, √{square root over (2)}/2 of thefield amplitude of the first pulse 1438A is combined with √{square rootover (2)}/2 of the field amplitude of the second pulse 1438B so thepower in the coincidence pulse 1438 is double the power of either thefirst or second pulse 1438A, 1438B. The energy at the non coincidenceoutput 1406A is zero and thus the total energy in the coincidence pulsesof the inputs is preserved at the outputs.

It should be noted that the pulses in FIGS. 23G and 23H are presented bytheir intensity and their phase as illustrated by the phase arrows asdiscussed above.

Referring to FIG. 23I, the pulses spacing and the relative phases ofspaced pulses can be used to create a symbology for selecting outputports. Each pulse duplicator (1456A–1456F) output port is characterizedby a pulse spacing, which selects a gate as discussed with regard toprevious embodiments, and the relative phases of the pulses selects oneof two output ports of the gate. A multiplexer receives pulses from asource, for example a mode locked laser as indicated at 1454. As inprior embodiments, the pulses can be duplicated by a pulse duplicator1465 (similar to duplicator 803D of FIG. 15C) to increase their densityand distributed by a manifold 1464 to multiple parallel channels 1462(typ.) such that pulses are applied to each channel 1462 (typ.), perhapswith a respective delay relative to those applied to the other channels1462 (typ.) Relative delays (for interleaving) may be introduced by wayof delays 1460A–1460F in respective channels 1462 (typ.). The modulators1453 (typ.) control whether a pulse passes or not on a specific channelas required by a source signal 1450 (typ.) which may represent separatesignals or elements of a single signal (vector).

Pulse duplicators 1456A–1456F each duplicate an output pulse from arespective modulator 1453 (typ.) with a unique combination of pulsespacing plus phase difference as indicated by symbols 1470A–1470F. Thelatter are interleaved onto a common channel 1481 by a combiner 1468which transmits it to a receiver 1482. The received signal from commonchannel 1481, which may be miles long or just a fraction of an inch, isdistributed among multiple gates, exemplified by three 1471, 1472 and1473. Each gate 1471, 1472 and 1473 has two outputs: 1471A and 1471B forgate 1471, 1472A and 1472B for gate 1472, and 1473A and 1473B for gate1473. Each output 1471A and 1471B for gate 1471, 1472A and 1472B forgate 1472, and 1473A and 1473B for gate 1473 corresponds to a particularsymbol 1470A–1470F such that only one will produce a coincidence pulsewhen a given symbol is sent through the common channel 1481. Each output1471A and 1471B for gate 1471, 1472A and 1472B for gate 1472, and 1473Aand 1473B for gate 1473 corresponds to a unique combination of pulsespacing 1542 indicated by time Δt (typ.), which selects one gate 1471,1472 or 1473 and phase difference 1544 indicated by the phase φ (typ.)between the pulses, which selects the output 1471A or 1471B if gate 1471is selected, 1472A or 1472B if gate 1472 is selected, or 1473A or 1473Bif gate 1473 is selected. Note that pulses drawn upside down represent aphase shift of π radians.

As will be evident from the above description by using a combination ofphase and time delay, the number of outputs that can be selected can bedoubled over using time delay alone. Also, the dilution of signal energyis reduced by half because the pulse intensity is preserved across agate that adds coherently and energy does not have to be diluted amongports of a given gate.

Referring now to FIG. 23J, a multiplexer 1521 places the signals fromeight data channels 1519A–1519H (the number of channels beingarbitrarily chosen for illustration) onto a single data channel 1531 inwhich each channel is “labeled” with different symbols 1540A–1540Hconsisting of a combination of pulses with respective phaserelationships. Referring momentarily in particular to FIGS. 23K and 23M,each symbol, here exemplified by that for channel 1519A has eight pulsesP1–P8. The first four pulses P1–P4 are summed as indicated by therelationship between signals 1543A and 1543B to produce a coincidencesignal (plus artifact) as indicated at 1543C. This summing occurs in thefirst gate 1530 of a binary tree structure of FIG. 23J.

Referring now also to FIGS. 23K, 23L, 23M in particular, in the examplesignal 1540A and another sample signal 1540G, high-going pulses such asP10 of FIG. 23L represent pulses with a particular phase angle andlow-going pulses such as P11 of FIG. 23L represent pulses with a phaseangle that is π radians ahead, or behind, that of high-going pulses suchas P10. The first four pulses P1–P4 of symbol 1540A are summed(summation shown at 1547A) based on a time difference such that the timeshift is indicated by the relationship between signals 1543A and delayed1543B (as shown at 1547A) to produce a coincidence signal (plusartifact) as indicated at 1543C. That is, the time shift (internaldelay) of the first gate 1530 is equal to the spacing between pulse P1and P5. The resulting coincidence signal 1543C emerges from one of theoutputs of gate 1530, in the embodiment, output 1530A of FIG. 23J. Thecoincidence signal 1543C contains a portion 1543I that results fromsumming so it is enhanced with the remainder being non-coincidence andso its amplitude is diminished. If P1–P4 had the opposite phase, thesumming would have produced the coincidence signal from output 1530Binstead of output 1530A.

Another summation 1547B occurs in gate 1533, which results in acoincidence signal 1543E and is output from output 1533A. Finally, yetanother summation 1547C occurs in gate 1535, which results in a finalcoincidence signal 1543G and is output from output 1535A. It will beobserved from the foregoing that the height of the coincidence pulse1543H incurs substantially zero degradation through the gates 1530, 1533and 1535 at ports 1530A, 1533A and 1535A, respectively, because phase isused to perform the gating through the successive layers.

It may be confirmed by inspection that the various pulses patterns1540A–1540H shall propagate accordingly:

Pattern 1540A will produce a coincidence pulse at output 1535A asdiscussed above.

Pattern 1540B will choose output 1530B, but will thereafter propagatethrough 1532A and out from output 1539A.

Pattern 1540C will choose output 1530A of gate 1530 and output 1533B ofgate 1533 and then output 1537A of gate 1537.

Pattern 1540D will choose output 1530B of gate 1530, output 1532B ofgate 1532 and output 1541A of gate 1541.

Pattern 1540E will choose output 1530A of gate 1530, output 1533A ofgate 1533 and output 1535B of gate 1535.

Pattern 1540F will choose output 1530B of gate 1530, output 1532A ofgate 1532 and output 1539B of gate 1539.

Pattern 1540G will choose output 1530A of gate 1530, output 1533B ofgate 1533 and output 1537B of gate 1537.

Pattern 1540H will choose output 1530B of gate 1530, output 1532B ofgate 1532 and output 1541B of gate 1541.

As may be also be confirmed by inspection, the above binary tree formatmay be extended to any number of final outputs and the eight shown herewas a number arbitrarily chosen for illustration.

Referring to FIG. 23N, as in the embodiment of FIG. 23I, a combinedpulse-spacing Δt_(k) and phase-difference Δφ_(j) construct encodedsymbol (code) 1589 (a phase-difference symbol Δφ_(j) being thedifference between the phases of two pulses forming a pulse pair and apulse spacing Δt_(k) symbol being the temporal spacing of the two pulsesof a pulse pair) may be employed to advantage for switching. Also, asdiscussed above, phase difference of pulses alone can be employed forswitching. A generalization of these systems is illustrated by FIG. 23P,which shows a generalized receiver 1549. A signal 1580A containingpulses is applied by means of a distributor 1580B to an array of gates1583A, 1583B, 1583C of arbitrary number. Each gate has two respectiveoutputs OA1, OB1, OC1 and OA2, OB2, OC2. These outputs OA1, OB1, OC1 andOA2, OB2, OC2, may be connected to successive layers of gates (notshown) as illustrated in previous embodiments.

In one embodiment, each gate 1583A, 1583B, 1583C of FIG. 23P maycorrespond to a unique combination of pulse spacing Δt_(k) and phasedifference Δφ_(j) and employ only one of the illustrated outputs, forexample OA1, OB1, OC1. Referring also to FIG. 23Q, in this case weassume the number of phase differences between pulse pairs 1589 of FIG.23N, as well the pulse spacing is arbitrary. For example, let there befour phase differences permitted, 0, π/2, π, and 3π/2. If a pulse pairsymbol arrives at a given gate, it will only potentially produce acoincidence pulse if the pulse spacing matches the gate. In the presentsystem, we have assumed that there are four possible phase differencesbetween the pulses in a pulse pair so there would be four gates for eachpulse spacing, each with the same time delay to match the pulse spacing,but each having a unique phase difference between adjacent pulses.Therefore the number of gates may be the number of allowed pulsespacings multiplied by the number of allowed phase differences. A chartC1 of FIG. 23Q indicates the intensity levels that are output by a gatewhose pulse spacing Δt matches that of a symbol, but whose phase shiftΔφ differs by the indicated Δφ_(G)−Δφ_(P), which is the differencebetween the gate phase difference (i.e., shift) Δφ_(G) and the signalphase difference Δφ_(P). This intensity is proportional to2[1+cos(Δφ_(G)−Δφ_(P))]. Again, it is assumed the spacing of the pulsesis such that the gate's time delay Δt would cause them to produce acoincidence pulse assuming phase alignment; i.e., that the pulse spacingmatches that of the delay within the gate.

In the example, there are four possible relationships between the phasedifference Δφ_(P) of a pulse-pair symbol and the phase shift Δφ_(G)integral to the delay of a gate 1583A, 1583B, 1583C:

-   1. the gate delay includes a phase shift that differs from the    difference in the phases of the pulses by 0 radians;-   2. the gate delay includes a phase shift that differs from the    difference in the phases of the pulses by π/2 radians;-   3. the gate delay includes a phase shift that differs from the    difference in the phases of the pulses by π radians; and-   4. the gate delay includes a phase shift that differs from the    difference in the phases of the pulses by 3π/2 radians.

In chart C1, if the phase difference of the pulses differs from theshift imposed by the gate by 0 radians (i.e., they match perfectlyΔφ_(G)−Δφ_(P)=0) the intensity of the coincidence pulse at therespective output OA1, OB1, OC1 (i.e., the one satisfying the first ofthe four conditions listed above) is 4 in arbitrary units as indicatedat δ1. If the phase difference differs from the gate by π/2 or 3π/2(i.e., Δφ_(G)−ΔφP=π/2 or 3π/2) the intensity of the coincidence pulse atthe corresponding outputs among OA1, OB1, OC1 is 2 in arbitrary units asindicated at δ2 and δ3, respectively. If the phase difference differsfrom the gate by π, the (i.e., Δφ_(G)−Δφ_(P)=π), the intensity of thecoincidence pulse at the corresponding output OA1, OB1, OC1 is 0 inarbitrary units as indicated at δ4.

According to an example protocol, only pulses with an intensity of 4constitute passing the signal. Thus, any mismatch in phase would resultin the blocking of the signal. In previous embodiments, it was discussedhow artifact may be eliminated either by detection, threshold or byoptical filtering and any of those may be used, electronically oroptically, to eliminate signal resulting from phase mismatch. In otherwords, signals δ2δ4 may be treated as artifact and filtered ordiscriminated as discussed above with regard to artifact pulses.

In an alternative embodiment, both respective outputs OA1, OB1, OC1 andOA2, OB2, OC2 of the gates 1583A, 1583B, 1583C of the receiver 1549 ofFIG. 23P are employed. This allows some gates to be eliminated. Considera system in which a first gate is selective of a first pulse phasedifference so that it outputs a maximal coincidence pulse at its firstoutput port (e.g., corresponding to δ1 in FIG. 23Q) when the first pulsephase difference is applied to it and a second gate is selective of asecond pulse phase difference so that it outputs a maximal coincidencepulse at its first output port (e.g., corresponding to δ1 in FIG. 23Q)when the second pulse phase difference is applied to it. Now considerthe situation where the first and second pulse spacings differ by π. Thesecond output of the first gate will produce a maximal coincidence pulsewhen the second pulse phase difference is applied to it and the secondoutput of the second gate will produce a maximal coincidence pulse whenthe first pulse phase difference is applied to it. Thus, the secondoutput of the first gate generates the same output as the first outputof the second gate, which means the second gate can be eliminated.

In the present embodiment, rather than providing separate gates forpulse-pair symbols whose phase differences differ by π, one gateprovides outputs for both. Thus, when a pulse pair has a phasedifference of 0 radians, one of the outputs OA1, OB1, OC1 will beselected and when the phases of pulses differ by π radians, the other ofthe outputs OA2, OB2, OC2 will be selected. This is because, asdiscussed previously, where the maximal coincidence pulse is generatedat a first output of certain types of gates when the phase differenceΔφ_(j) of the input code (having index j) is of a certain relationshipsuch that the pulses of the code totally reinforce each other throughthe first output and completely cancel each other at the second output,a change in the phase difference Δφ_(j) of the code by π will cause thepulses of the input code to cancel each other at the first output andtotally reinforce each other at the second output. Thus, in a four phaseprotocol, if a maximal coincidence output is generated when the pulsesof the input code are at 0 phase difference (zero being arbitrarilyassigned, since in the present discussion, the only attributecontemplated is the difference in phase when the pulses of the inputcode are merged into the same channel such that they interfere, anyarbitrary amount of change of phase being possible from the inputs ofthe gates to the point at which the signals are merged being possible)then a difference in phase between the pulses of the input code eitherby π/2 or 3π/2 would produce a low level signal at both outputs of thegate since a phase difference of π selects only one output (the othergate's output is 0) while a phase difference of 0 only selects the otheroutput (the first gate's output is 0).

Referring to FIG. 23R, in a further variation, time spacing of pulses islimited to a single spacing such that all gates in a receiver such as1549 (FIG. 23P) have identical delays Δt but different phase shiftsΔφ_(G). In such an embodiment, each pulse, for example 1587B, defines aphase difference relative to a preceding pulse, for example 1587A. Thepulse spacing is identical for all pulses and equal Δt so that everygate produces time coincidence but, a maximal coincidence signal isproduced only when the phases Δφ_(j) of (images of) adjacent pulses aremerged within the gate with a phase difference Δφ_(G)−Δφ_(P) of zero.Thus, each gate has a delay equal to Δt and a specific phase shiftΔφ_(G). For each gate j there is a specific phase shift Δφ_(Pj) betweenadjacent pulses at the input that results with phase relationshipsΔφ_(Gj)−Δφ_(Pj)=0 producing a maximum (main) coincidence signal only atgate j. Accordingly, the value of the phase shift between adjacentpulses dictates at which of the gate a main coincidence signal isproduced.

Thus, each pulse is coincident in time with its successor to form a newoutput based only on the phase difference of a pulse with the adjacentpulse with which its own image is made to be coincident with itsneighbor's image. A main coincidence signal is produced only at thespecific gate corresponding to the specific phase different betweenadjacent pulses that fulfill Δφ_(Gj)−Δφ_(Pj)=0 Thus, the signal 1587C iscoincident with its delayed version 1587D producing main coincidencepulse at different gates according to the different phase shifts betweenthe adjacent pulses at the input. Thus, every pulse cooperates to form asymbol by the spacing and phase difference from its predecessor as wellas a symbol by the spacing of its successor. This means that each pulsehas double duty to serve both, as an information pulse (being the firstof each pair of adjacent pulses) and as a control pulse (being thesecond of each pair of adjacent pulses).

In an example configuration, if four allowed phase differences aredefined, four possible output ports may be selected. This phasemodulation may be obtained by any of the, above-described modulationtechniques.

According to the foregoing description, the highest amplitudecoincidence pulse is produced at the gate's output when both timecoincidence and phase coincidence occur at a gate. Time coincidenceoccurs when the temporal spacing of a pulse pair equals the delay of agate. Phase coincidence occurs when the difference between the phases ofthe symbol's pulses is such that the gate produces a maximal coincidence(Δφ_(Gj)−Δφ_(Pj)=0) between the delayed and direct images of the pulsesin a pulse pair.

Referring to FIG. 23S, in an example application of the phase-onlymodulation scheme discussed with reference to FIG. 23R, a pair ofsignals S₁ and S₂, which may or may not be synchronous, arrive at amultiplexer 1591A and are modulated such that every pulse 1596A (typ.)(for example, each representing a bit) represents data encoded as a oneof several allowed phase differences existing between itself and anadjacent pulse with which it is made to be coincident in a gate (notshown) of a demodulator 1591B. Modulated signal 1596A is a single streamof pulses propagating in single guide 1593 and is encoded to include theinformation of both streams of signals 1590A and 1590B. The pulses 1596Amay be spaced at regular intervals which means a single gate time delaycan be used in which each pulse produces a coincidence output. Thus,each pulse represents data in the form of the phase difference betweenan image of itself and a delayed image of its predecessor pulse thatcoincide in a gate, i.e., each represents a single phase-differencesymbol. The pulses could be samples from a single signal S₁ or S₂ or onefrom each signal S₁ and S₂ which may require the use of a buffer if thesignals S₁ and S₂ are not synchronous. Assume the followingcorrespondence between phase-difference symbols and bit pairs:

TABLE 2 Example of a Phase-difference symbol map for two synchronousdata streams Phase difference between two adjacent pulses S₁ S₂ in asignal stream carried by guide 1593 0 0 Δφ₁ = 0 0 1 Δφ₂ = π/2 1 0 Δφ₃ =π 1 1 Δφ₄ = 3π/2

Assume one pulse from each channel is used to form the symbol asindicated in the above table. Thus, the first pulses of the signalstreams 1590A (S₁) and 1590B (S₂) are 1 and 0, respectively. The phasedifference symbol modulated on the channel 1593 by modulator 1591A wouldthen be Δφ₃=π. The next pulses of the signal streams 1590A and 1590B are0 and 1, respectively, so the phase difference symbol modulated on thechannel 1593 by modulator 1591 A would then be Δφ₂=π/2. The nextrespective pulses of the signal streams 1590A and 1590B are 1 and 0again so the phase difference symbol modulated on the channel 1593 bymodulator 1591A would then be Δφ₃=π. The next pulses of the signalstreams 1590A and 1590B are 1 and 1, respectively, so the phasedifference symbol modulated on the channel 1593 by modulator 1591A wouldthen be Δφ₄=3π/2. The next pulses of the signal streams 1590A and 1590Bare 0 and 0, respectively, so the phase difference symbol modulated onthe channel 1593 by modulator 1591A would then be a Δφ₁=0.

The signal 1593 is first demodulated by a demultiplexer 1591B, which maybe configured for example, as the demultiplexer device 1549 of FIG. 23Pto generate four data streams of coincidence pulses 1594A–1594Dcorresponding to the four phases of modulation used to encode signal1596A. The latter four streams 1594A–1594D may then be modulated by amultiplexer 1591C onto respective channels 1597A and 1597B applied torespective receivers R₁ and R₂. The multiplexer 1591C may convert thesignals from their form on the channels 1597A and 1597B, e.g., optical,to electronic form to permit reconstruction using any of the modulationschemes discussed above. Thus, each pulse pair symbol arriving fromchannel 1593 produces a pair of pulses from the original signals 1590Aand 1590B at inputs S₁ and S₂, respectively, thereby providing a 2:1compression ratio.

Referring now to FIG. 23U, the phase difference between adjacent pulsesdiscussed so far can be any number of phase differences provided thecapability of discriminating the intensities of coincidence pulses isenabled. The teachings of the present specification include variousmethods of providing some minimum threshold such that coincidence pulsesgenerated from, for example, incident pulses differing in phase byΔφ_(G)−Δφ_(P)=π/3 or more, are distinguished from coincidence pulsesgenerated from incident pulses differing in phase by Δφ_(G)−φ_(P)=0. Ina scheme in which pulses can differ by six possible phase angles, thehighest coincidence pulse intensity still results from a perfect matchof a gate's phase shift to the phase difference between pulses in apulse pair. However, the next-best match, in a gate whose phase shift isone sixth of 2π, or π/3, produces a coincidence pulse whose intensity is75% (as discussed below) of that of a perfect match. Here, a chart C2shows the intensities of coincidence pulses resulting from variousdifferences between phase difference symbols and gate phase shifts(Δφ_(Gj)−φ_(Pj)).

Referring also to FIG. 23P, in another embodiment, each gate 1583A,1583B, 1583C may correspond to a unique combination of pulse spacing andphase difference symbols and employ only one of the illustrated outputs,for example OA1, OB1, OC1 or both outputs may be used OA1, OB1, OC1,OA2, OB2, OC2 as discussed above with reference to FIGS. 23P–23Q. Inthis case assume there are six phase differences permitted, 0, π/3,2π/3, π, 4π/3 and 5π/3. If a pulse pair symbol arrives at a given gate,it will only be potentially passed if the pulse spacing matches a port.Chart C2 indicates the intensity levels that are output by a gate whosepulse spacing matches that of a symbol, but whose phase spacing differsby the indicated Δφ_(G)−Δφ_(P). Again, this intensity is proportional to2[1+cos(Δφ_(G)−Δφ_(P))], where Δφ_(G)−Δφ_(P) is the difference betweenthe gate phase difference (shift) and the signal phase difference (whenthey interfere). The spacing of the pulses may be made such that thegate's time delay would cause them to produce a coincidence pulseassuming phase alignment; i.e., that the pulse spacing matches that ofthe delay within the gate.

In the example, there are six possible relationships between the phasedifference of a pulse-pair symbol and the phase difference of a gate1583A, 1583B, 1583C. In the chart C2, if the phase difference differsfrom the phase shift of one of the gates by 0 radians (i.e., they matchperfectly) the intensity of the coincidence pulse at one of the outputsOA1, OB1, or OC1 is 4 in arbitrary units as indicated at δ5. If thephase difference differs from one of the gate by π/3 or 5π/3, theintensity of the coincidence pulse at the outputs of these gates OA1,OB1, or OC1 is 3 in arbitrary units as indicated at δ6 and δ7,respectively. If the phase difference differs from the gate by 2π/3 or4π/3 the intensity of the coincidence pulse at the outputs of thesegates OA1, OB1, or OC1 is 1 in arbitrary units as indicated at δ8 andδ9. Finally, if the phase difference is π, the coincidence pulse is 0 asindicated at δ0. Again, signals δ6–δ9 and δ0 may be treated as artifactand filtered as discussed above with regard to artifact pulses that maybe removed using electronic or optical threshold mechanisms.

FIG. 23Y shows a train of pulses 1504 that are modulated with phasedifference symbols. The stream of pulses 1504 is received by acoincidence gate 1502, which causes an image of each pulse 1505 (typ.)to be coherently added (with or without a phase shift) to an image of aneighboring pulse 1505 (typ.), which will obtain when the gate 1502delay matches the pulse 1505 spacing. The phase of each differs from theneighbor's by one of several permitted phase differences Δφ_(P) suchthat the coherent summing produced by the gate 1502 produces coincidencepulses of certain discrete magnitudes, each corresponding to a one ofthe permitted phase differences Δφ_(P). The phase shift Δφ_(G) producedby the gate 1502 may be calibrated to such magnitude as to maximize thedistinctiveness of the possible coincidence pulse magnitudes for eachpulse spacing Δφ_(P) thereby making it possible to classify eachcoincidence pulse by magnitude. For example, this may be done if therange of the allowed differences between gate phase shift Δφ_(G) andpulse phase difference Δφ_(P) is maximized by including in the allowedvalues of Δφ_(P) those values such that Δφ_(G)−Δφ_(P) includes thevalues of 0 and π, where Δφ_(G) is fixed and produces a coincidencepulse with an amplitude that is unique for each relative phase Δφ_(P).The other pulse phase difference Δφ_(P) values may be equidistantbetween those values or may be values such that the magnitudes of thecoincidence pulses they produce are equidistant. That is, the series maybe Dφ_(P,j)=α cos [j(1−2/(N−1))] where j=0 through N−1. Otheralternatives are possible, as long as the magnitudes aredistinguishable. For example, the range cover equal steps in phase anglebetween 0 and π as example by N=4 to produce 0, π/3, 2π/3 and π. Notethat there are two solutions for each element of the series Δφ_(Pj)between (and not including) 0 and π and either may be used for eachelement of the range.

As an example, the series using N=4 may be used to produce fourdistinguishable magnitudes for the coincidence output, eachcorresponding to a respective phase difference in the signal Δφ_(P). Adetector has an optical sensor 1598P and magnitude classifier 1598L,which may function as a window discriminator for distinguishing betweenthe different values of the amplitudes of the coincidence signalsproduced by gate 1502 and are illustrated by C3. Chart C3 has apresentation similar to chart C2 of FIG. 23U. The possible magnitudestates in the output signal 1503A, as illustrated, are 0,a[cos(⅓)]=0.34a, a[cos(⅔)]=0.73a, and π, where a is the amplitude of thepulses of the encoded signals at input 1599Q of gate 1502.

The embodiment of FIG. 23Y may be used for compression as described withreference to FIG. 23S, with multiple bits of one or more streams aresymbolized by a single phase-difference symbol using the N-levelembodiment described with reference to FIG. 23Y. The compression may beobtained by using the N-level embodiment of FIG. 23Y in which eachcoincidence pulse may get N different values. In such an application thecompression is given by log(N)/log(2).

Note that in the above discussions where phase differences were assumedbetween pulse-pair symbols, it should be clear that polarization-basedembodiments would function in an analogous manner and may be substitutedin all such cases. Thus, all discussion and drawings in which thecoincidence gates are triggered by phase modulation may also betriggered by polarization modulation. For example, the vector diagramsin the various drawings may represent either relative phases or relativepolarizations of the pulses making up symbols. The behavior and outcomeare the same in both cases. Fur example, the vectors illustrated inchart C3 of FIG. 23Y may represent a state of relative phase or relativepolarization orientation.

Referring now to FIG. 24, an optical oscillator 1740 generates a seriesof pulses that are distributed to various gated channels 1745A–1745D,each including a gate 1756 (typ.). One input of each gate receives apulse from the optical oscillator 1740 whose duty cycle is equal to theinverse of the number of channels 1745A–D. The pulses from the opticaloscillator 1740 are delayed by a respective delay for each channel1745A–D by a respective one of the delay elements 1743A–D. The delaysare such as to cause a control pulse 1747 (typ.) arriving from theoptical oscillator 1740 to be coincident with every N^(th) pulse datapulse in a signal pulse 1746 (typ.) arriving from a data source such asa multiplexer indicated generally at 1775. The power levels and phaseangles in the circuit shown may be such that the each data pulse isenhanced by (i.e., generates a coincidence output from a respectivetypical gate 1756 due to its coincidence with) the pulse from opticaloscillator 1740. Thus, the optical oscillator 1740 may be said to sampleor take a snapshot of a different pulse on each channel that isrespective to the particular time slot coinciding with the arrival ofthe oscillator pulse. It will be apparent to those of skill in the artand in view of the present disclosure that the outputs on each channel1745A–D each corresponds to a time division demultiplexing (TDM)multiple access (TDMA) channel. The artifact pulses that may exist inthe TDM channels may be eliminated by the different methods discussedabove.

To generate a signal for use in such a TDM system, a multiplexer that issimilar to the embodiment of FIG. 15C and other embodiments discussed orwith similar functionality may be employed. Here multiplexer 1775 hasmultiple modulators 1751 (typ.) that are controlled by signal sources1749 (typ.) to selectively permit the passage of pulses from a pulsesource 1758A (which may include one or more pulse duplicators 1753 toincrease the pulse density). The pulses permitted to pass by themodulators 1751 (typ.) are interleaved onto a common channel accordingto respective time delays 1750 (typ.) Note that the result ofdemultiplexing in the embodiment of FIG. 24 is that there is no need forpulse-spacing symbology since regular time division channels areemployed. However, synchronization recovery and phase control may berequired to ensure alignment of received pulses with locally generatedpulses and coherent summing in the gates 1756 (typ.) Referring now toFIG. 25A, a mechanism for switching multiple data pulses using a singlesymbol representing an address (header), for example a spaced-pulsesymbol, for control, is shown. A signal 1550 includes a series of datapulses 1560 trailing behind a single address symbol 1553. The addresssymbol 1553 corresponds to a respective output channel. The addresssymbol generates a coincidence pulse when the address symbol 1553corresponds to the address (time delay Δt) of coincidence gate 1554,designated as “Address response”. The coincidence pulse is output fromaddress response coincidence gate 1554 on a distributing headercoincidence signal 1564 which may be amplified by amplifier 1563, andapplies a share of its energy to each of a set of coincidence gates1556A–1556E. Each of the delay channels 1558A–1558E receives a share ofthe energy 1555 from the incoming signal 1550 by way of distributingdata and header pulses 1555. Each delay channel 1558A–1558E delays arespective signal 1570A–1570E (an image of 1550) such that a respectiveone of the pulses indicated by highlighting 1568 is incident on arespective coincidence gate 1556A–1556E when the coincidence pulse 1564from the address response coincidence gate 1554 arrives at therespective coincidence gate 1556A–1556E. The propagation delays of thevarious channels defined by the distributing headers and data 1564 and1555 are such that the each channels respective pulse 1560 and thecoincidence pulse 1564 are precisely synchronized. Automatic phasecorrection may be required and introduced as indicated by way of examplein foregoing embodiments to ensure that a coincidence pulse is outputwhen a data pulse 1560 is coincident with the address coincidence pulse1564. Therefore the entire configuration of FIG. 25A operates as acoincidence gate for an entire payload of pulses 1560 controlled by asingle address symbol 1553. The pulses passed by the coincidence gates1556A–1556E are further interleaved onto a single channel 1785 by aconsolidation header 1784 configured with proper delays (not shown) tocause a passed signal to provide the same inter-pulse spacing as theoriginal signal 1550.

Referring now also to FIG. 25B, to create a switch using theconfiguration of FIG. 25A, it should be apparent from the abovedescription together with the teachings of foregoing embodiments thatthe entire configuration of FIG. 25A (cell coincidence gate 1551) may beused to gate cells (packets) 1550 (payload 1560 with or without theheader 1553), for a single channel, for example 1551A. Respective cellcoincidence-gates 1551A–1551C block or pass cells 1550 arriving on acommon channel 1788 and distributed by a distributor 1787 to each cellcoincidence-gate output channel 1551A–1551C. Passed cells are output toeach possible destination 1786A–1786C depending on the addressconfiguration for the cell coincidence gate 1551A–1551C as describedwith reference to FIG. 25A. Coincidence gates similar to coincidencegates 1556A–1556E (FIG. 25A) may also be provided for permitting theaddress symbol 1553 to be transmitted onto the channel 1786 withsuitable increase in the number of channels 1558A–1558E.

Referring now to FIGS. 25C, 25D, and 25H, the embodiment of FIG. 25A maybe described more schematically as including an address coincidence-gateto produce a coincidence pulse and apply it to a mechanism 1773, asillustrated by FIG. 25H, for mapping the coincidence pulse to one ormore coincidence gates 1774 (FIG. 25H). In FIGS. 25C and 25D, the cells(packets) include headers 1776A and 1585 and payloads 1776B and 1586,respectively. Pulses 1579A and 1579B of the header symbol are separatedby time space Δt_(h) corresponding to the time delay of the specificcoincidence-gate of this header. The payload has a length that is equalto Δt_(p). between pulses 1578A and 1578B. The pulse width of thepayload pulses, the header pulses and the spaces between these pulses isΔt_(x) wide. Images of the pulse stream of FIG. 25 are transmitted toeach of the address coincidence gate 1772 and a delay device 1777 ofFIG. 25H. The latter is configured to ensure that the output of themapping mechanism 1773 coincides with one or more coincidence gates 1774(FIG. 25H). Schematically, the mapping mechanism may be considered tosubsume within it the delay device 1777, since it cooperates in themapping process. The foregoing description relating FIG. 25C appliesalso to the embodiment of FIG. 25F discussed below.

Referring now also to FIGS. 25D and 25E, a scheme may be used to preventdata pulses 1560 (FIG. 25A) from generating address coincidence pulsesin header coincidence-gate 1554 (FIG. 25A). This may be necessary if itis desired to prevent payload pulses 1560 from causing an undesiredgating effect. A variety of mechanisms for preventing this are possible,such as a straightforward yet ineffective scheme of using separatephysical channels to carry the address and payload signals. Two schemesthat effectively avoid the generation of address coincidence pulses areshown in FIGS. 25C and 25D.

In FIG. 25C, the address symbol is assumed to be a spaced-pulse typesymbol in which the spacing of pulses 1579A and 1579B are permitted tobe only at even integral multiples of a predefined interval Δt_(x).Payload pulses 1578B (typ.) are permitted to be placed only odd integralmultiples of the predefined interval Δt_(x). The above protocol wastesevery other time slot for the payload data but reduces the overhead foreach data pulse substantially by permitting switching via a singleaddress symbol. It can be seen that the foregoing embodiments may beused with non-coherent types of coincidence gates.

Another way to avoid triggering address coincidence pulses by payloadpulses 1550 is to configure the address response coincidence-gate 1554of FIG. 25A so that constructive interference occurs only when there isa certain phase relationship between the two pulses forming the addresssymbol 1584A and 1584B (FIG. 25D). Here the relative phases of pulses isindicated by the arrows 1592 (typ.) with oppositely directed arrowsbeing π radians out of phase. The address response coincidence-gate 1554of FIG. 25A is configured to produce a coherently coincidence pulse whensimultaneously-incident pulses have the relationship illustrated bypulses 1584A and 1584B. It follows that if the address responsecoincidence-gate 1554 is so-configured, pulses with the relationship of1582A and 1582B will cancel and produce no coincidence pulse in theaddress response coincidence-gate 1554. It can be confirmed byinspection therefore that the only way to produce a coincidence pulse inthe address response coincidence-gate 1554 is the pair of pulses 1584Aand 1584B. Thus, no pulses other than those forming the address symbolwill generate an address coincidence pulse. Other combinations willdestructively interfere in the address response coincidence-gate 1554.

Note that another way of preventing payload pulses from generating acoincidence output in the address header is to polarize the pulsesdifferently in a manner that is analogous to the discussion of FIG. 25D.That is, the arrows 1592 would represent polarization instead of phase.

Referring now to FIG. 25E, an alternative configuration for switching apayload 1618A of an arbitrary number of pulses using a single addresssymbol 1619A uses a single coincidence gate for the entire switchedsignal. An input signal 1621 (including header 1619A and payload 1618A)is applied to a junction 1606 that divides some of the energy of theinput signal 1621 to send an image 1621B (including header 1619C andpayload 1618C) thereof to an address coincidence-gate 1607 and acorresponding image 1621 A (including header 1619B and payload 1618B)through a delay line 1605 with delay device 1608 (e.g., delay loops).The image sent to the address coincidence-gate 1607 generates acoincidence pulse 1620P if the address symbol portion 1619C (image of1619A) matches the address coincidence-gate 1607 configuration (forexample, a spaced-pulse symbol). This works in a manner that isidentical to that disclosed with respect to FIGS. 25A–25D. Thecoincidence pulse 1620P may be amplified by an amplifier 1611 and theresulting output pulse 1620A expanded temporally by duplicating it witha pulse duplicator 1601A to yield a broadened pulse 1620B. Successiveexpansions by duplicators 1601B and 1601C result in successively broaderpulses 1620C and 1620D, respectively. Although not illustrated, theduplication process may necessarily result in a diminution in amplitudein the resulting expanded pulse. Such diminution may be compensated byamplifier 1611.

Referring also to FIGS. 25E, 25F and 25G, the width T of the pulse 1620Dmay be as great as the images 1621A–1621B of the received signal 1621.The timing delay of the delay line 1605 is arranged such that theleading edge of signal 1621A and the leading edge of broad pulse 1620Dare both incident on coincidence gate 1603 at the same instant. Thepulse 1620D and signal 1621A produce coincidence pulses in thecoincidence gate 1603 for each pulse in the signal 1621 because thebroad pulse 1620D overlaps all of them. Such a situation is illustratedby FIG. 25G which shows that pulse 1620D (having a width T) is wideenough to produce coincidence, at gate 1603, with all the pulses of thesignal 1621A (including payload 1618B and header 1619B). The width T ofpulse 1620D may be adjusted to exclude header 1619B (1619A). In such acase, only payload 1618B (1618A) will be transmitted by coincidence gate1603.

The output of the coincidence gate 1603 will be an image of the incomingsignal 1621 if address symbol 1619C (1619A) produces a coincidence pulsein the address coincidence-gate 1607. This is because the broad pulse(FIG. 25E or FIG. 25G) generated by the address coincidence-gate 1607and duplicators 1601A–1601C is coincident with every pulse of the signal1621. If the address symbol does not generate a coincidence pulse, nocoincidence pulses are generated in the coincidence gate 1603 andtherefore the signal 1621 may be said to be blocked by the apparatus ofFIG. 25E. Only the address symbol 1604 (FIG. 25F) may generate acoincidence pulse 1615 in the address coincidence-gate 1607 using somenon-interference scheme, for example the method of FIG. 25C which mayconfirmed with reference to FIG. 25F. The packet pulses 1602 do notgenerate a header coincidence pulse as can be seen from the relationsbetween signal 1608 and its delayed image 1609. This may be confirmed byinspection for the odd even pulse scheme discussed with reference toFIG. 25C.

Referring to FIG. 25J, another means by which data may be switched usingone or more coincidence gates 1774A is to resolve and actuate theaddress header 1776A electronically. For example, the address header1776A may be applied to an optoelectric detector 1772B to generateresponsive signals providing the address to a recognition circuit 1772Awhich controls one or more lasers or laser modulators 1779 that providesignals upon positive recognition to a mapping mechanism 1773A. Thelatter applies light to one or more coincidence gates 1774A. Eachcoincidence gate may correspond to a respective address in the presentconfiguration. Thus, laser or modulator 1779 may have multiple outputchannels, each carrying a signal to a different coincidence gate, thatmay output for the incoming data cell, including payload 1776B, and withaccordance to its header 1776A.

Referring to FIG. 25K, an alternative mechanism for employing a singlecoincidence gate to selectively block or pass a data cell (packet) 1621is to send the address coincidence pulse 1620P into a cascade of delays1640, having multiple leayers 1641 (typ.) connected in parallel, toproduce a series 1642 of differently delayed images of the coincidencepulse 1620P. The series 1642 is simultaneously incident on thecoincidence gate 1603 with the signal image 1621A. Those pulses in theimage 1621A that coincide with the pulses in the series will be passedby the coincidence gate 1603. Since the pulses in the image 1621A canonly be in certain locations, the pulses in the series 1642 may bearranged so that they always pass the pulses in the image 1621A as maybe confirmed by inspection of FIG. 25L which shows that each payload1618B is coincident with a particular series 1642 pulse thereby causingall the payload 1618B pulses to produce a coincidence pulse from thecoincidence gate 1603 and therefore transmitted out of coincidence gate1603. Although FIG. 25L illustrates only the payload 1618B being“transmitted,” it should be evident from the drawing and otherdescriptions that the series 1642 may be expanded to include the addresssymbol if desired.

Various techniques for canceling non-coincidence signals (artifacts)below a certain threshold level were discussed with reference to FIGS.12A–12K. The application discussed there was the elimination of sidepulses below a certain magnitude. Recall that these devices canceled allpulses below a certain magnitude that corresponded to some level definedby the nonlinear behavior of a piece of material or an opticalamplifier. Essentially, these devices pass only the portion of an inputsignal above a specified threshold. For example, in the embodiment ofFIG. 12A, an input signal applied at 614 would produce zero output at613A for all input signal magnitudes below a saturation level of theoptical amplifier 615. An input signal above the saturation level wouldbe reduced by level of the saturation (assuming unity gain, otherwisethe output above the saturation level would be magnified/reduced by thegain of the overall device). In other words, the cancellation devices ofFIGS. 12A–12K pass only the portion of the input signals above apredefined level corresponding to the nonlinear gain curve (e.g., FIG.12B or 12F) characterizing the cancellation device.

Referring now to FIG. 26A, a cancellation device 1651 exhibits thebehavior described above of passing only the portion of an input signalabove a threshold level. Activation and threshold inputs 1655A and 1655Breceived by terminals I and T, respectively, are combined coherentlysuch that they interfere destructively in a reverse Y-junction 1655C togenerate a combined signal 1655 representing the difference of theactivation and threshold signals 1655A and 1655B. The activation inputsignal 1655A and threshold input signal 1655B may be named thus becausethe threshold signal 1655B increases the magnitude the input signal mustreach in order to produce a positive signal 1655 at the output ofcombiner 1655C. Phase alignment effective to ensure the coherentsubtraction may require the use of a phase compensation devices 1659Aand one or more others within the cancellation device 1651.

In the embodiment of FIG. 26A, the combined signal 1655 is applied to acancellation device 1651, which may be as illustrated and described withreference to FIG. 12A, for example. The output signal 1664 from thecancellation device 1651 may be applied to an amplifier 1658A with highgain and nonlinear signal-limiting behavior (as described, for example,with reference to FIGS. 12B and 12F, so that any small output at 1664will be amplified at output 1656, by amplifier 1658A, to a saturationlevel of the amplifier 1658A.

The signal at 1655 represents a difference between the activation inputsignal 1655A and a threshold signal 1655B. The cancellation device 1651outputs only the portion of this difference signal 1655 above thethreshold determined by the type and configuration of the cancellationdevice 1651. The amplifier 1658A amplifies this output 1664 with highgain up to a level of another threshold corresponding to the saturationlevel of the amplifier 1658A. In other words, the output 1656 is clampedto the saturation level of the amplification 1658A when the activationinput signal 1655A goes above a level determined by the threshold signal1655B. Thus, the threshold signal 1655B may be used to vary theactivation input signal 1655A signal that triggers device 1650 output1656 to clamp to the saturation level.

Referring now also to FIG. 26B, the configuration of 1650 actssubstantially as a comparator 1670 with a threshold at a threshold input1654B causing an output 1674 to be near zero when a signal at an“activation” input 1654A is below a certain threshold level at thresholdinput 1654B. Comparator 1670 is responsive to an activation signal1654A, at output 1674, when activation signal 1654A is above the certainthreshold level 1654B. Thus, changing the threshold input 1654Beffectively raises or lowers the signal level required at the activationinput to trigger a high level output at 1674.

Referring again to FIG. 26A, in an alternative embodiment, thecancellation device 1651 is omitted and the difference signal 1655 isapplied directly to the amplifier 1658A. In this embodiment, the output1656 may not fall to zero if the activation input signal 1655A is belowthe level imposed by the threshold input 1655B. However, the effect ofthe threshold signal 1655B is still to raise and lower the level towhich the activation signal 1655A must rise to clamp the output 1656.Thus, its behavior is substantially similar to that of FIG. 26A.

Note that although not shown, phase alignment of the various signalsrequired to produce the effects discussed may be maintained by phaseshifters controlled by a controller in a closed loop (not shown)according to principles discussed in the present specification.

Referring now to FIG. 27A, a bistable (flip-flop) device 1865 has leftand right inputs 1687L and 1687R, respectively. Left and rightcomparators 1670L and 1670R, have respective threshold, L1T and R1T, andactivation inputs, L1A and R1A. The left and right comparators 1670L and1670R may be configured such that their respective outputs L2 and R2 arenot necessarily zero when in a low-output state, for example by using aconfiguration such as shown in FIG. 26A without the cancellation device1651.

Inputs L1A and L1T correspond, respectively, to activation and thresholdinputs 1654A and 1654B discussed with respect to FIG. 26B. Similarly,inputs R1A and R1T correspond to activation and threshold inputs 1654Aand 1654B discussed with respect to FIG. 26B. Signal subtractors(couplers) 1693A and 1693B coherently add incoming signals such thatthey destructively interfere. Thus, signal subtractors 1693A and 1693Bare configured to act as signal subtractors or inhibitors because a highlevel signal at L0 will inhibit a signal R3 propagating through thesubtractor 1693A. Similarly, a high level signal at R0 will inhibit asignal L3 propagating through the subtractor 1693B.

Signal taps 1690A and 1690B tap some of the signal energy in respectivefeedback lines 1692A and 1692B to provide outputs 1691A and 1691B,respectively. The taps 1690A and 1690B may include y-junctions,directional couplers, beam splitters or any suitable devices. Thepercentage of the energy tapped by them may be low and opticalamplification may be used to make the outputs 1691A and 1691B suitabledrivers for upstream processing (not illustrated). Lasers 1688A and1688B generate continuous constant signal levels. Although shown as twodevices they may indeed be a single laser source combined with asplitter or other source of narrow band light divided into multiplestreams by an optical header (not shown).

To understand the bistability of the circuit, one can assume for amoment that a first current stable state (R-high) exists in whichchannel 1692B carries a high level signal. The signal may be high enoughto raise the threshold input L1T to a level such that laser 1688A doesnot clamp the comparator 1670L output L2 to its maximum level. Thesignal at L2 will thus be at a low level. The low level signal L2propagates to L3, via guide 1692A, where it passes through subtractor1693B providing a low level threshold to comparator 1670R allowing laser1688B to clamp the output R2 to a high level. The signal at R2 thenpropagates to R3 where the cycle repeats. The device in theabove-described R-high state thus remains in that state and this stateis therefore stable. Assume a second current stable state (L-high) inwhich channel 1692A carries a high level signal that is high enough toraise the threshold input R1T to a level such that laser 1688B does notclamp the comparator 1670R output R2 to its highest level. The signal atR2 will thus be at a low level. The low level signal R2 propagates toR3, via guide 1692B, where it passes through subtractor 1693A providinga low level threshold to comparator 1670L allowing laser 1688A to clampthe output L2 to a high level. The signal at L2 then propagates to L3where the cycle repeats. The device in the second above-described statethus remains in that state and this state is therefore stable.

If a high level signal is applied at the left input 1687L while thecurrent state is R-high, the left input signal inhibits the signal at R3lowering the threshold input L1T. If the input on 1687L is sufficientlystrong, it causes the signal at L2 to reverse because it allows thelaser signal L1A to clamp the output at L2 to a high level. The L2signal propagates through the feedback channel 1692A thereby raising thethreshold for the right comparator 1670R and switching the state toL-high. If a high level signal is applied at the left input 1687L whilethe current state is L-high, nothing happens because the input simplyfurther diminishes the R3 signal causing the threshold level L1T tolower. The decrease in L1T does not substantially affect the intensityat output L2, which has already been clamped to a high level; evenbefore the high signal 1687L was applied to input L0 to lower thresholdL1T. If a low level signal 1687L were applied to input L0, even at aphase that caused the signal 1687L to be added constructively to R3 bysubtractor 1693A, it might still be insufficient to increase thethreshold L1T to a level that overcomes the laser signal at L1A andthereby would not cause device 1865 to change its state to R-high andthe device would remain in the L-high state.

If a high level signal is applied at the right input 1687R while thecurrent state is L-high, the right input signal inhibits the signal atL3, thereby lowering the threshold input R1T. If the input issufficiently strong, the signal at R2 will reverse allowing the lasersignal R1A to clamp the output at R2 to a high level. The R2 signalpropagates through the feedback channel 1692B thereby raising thethreshold for the left comparator 1670L and switching the state toR-high. If a high level signal is applied at the right input 1687R whilethe current state is R-high, nothing happens because the input simplyfurther diminishes the L3 signal to lower the threshold level R1T. Thedecrease in R1T results in no change in the intensity level at outputR2, which was already clamped to a high level even before a high signal1687R was applied to input R0 to lower threshold R1T. If a low levelsignal 1687R were applied to input RO, even at a phase that caused thesignal 1687R to be added constructively to L3 by subtractor 1693A, itstill might be insufficient to increase the threshold R1T to a levelthat overcomes the laser 1688B signal at R1A and, as a result, not causedevice 1865 to change its state to L-high.

The net gain (including amplifications, losses, and attenuations) alongthe complete optical loop that starts and ends at L3 and includes R2,R3, and L2 is preferable higher than 1. This helps to ensure bistableoperation. To make the intensity at the output 1691A or 1691B of device1865, when in a low state, close to zero, the clamped intensity at R2 orL2 may be made to have a magnitude similar to that received from thelasers 1688A or 1688B at L1A or R1A.

The bistable device 1865 of FIG. 27A, as should be clear from the abovedescription, acts as a stable memory cell in which the application of asignal at one input either switches it to a state corresponding to thatinput or has no impact if the state corresponding to that input alreadyexists. If the first input corresponds to a first state, a signalapplied to the first input ensures the device is in that state. Theoutput state is indicated by the signals of the outputs 1691A or 1691B.When on output 1691A (or 1691B) is high, the other output 1691B (or1691A) is low

Referring now to FIG. 27B, an alternative configuration for a bistabledevice is shown generally at 1810. As will be recalled, certain gatedevices may be configured such that the entire energy incident on bothinputs is emitted from one output or the other depending on the phaserelationship between the two signals applied at the inputs. For example,such a gate may include a dielectric beam splitter or a directionalcoupler. The bistable device 1810 employs a gate 1806 illustrated as adielectric beam splitter. Laser light from a laser source 1802 isincident at a first port 2706 of the gate 1806. Light from the laser1802 can follow one of two possible paths 2712 and 2714 to a second port2702. A right path 2712 goes through a first right junction 2710,through a second right junction 2720, through a phase shifter 2529,through a middle junction 2728, through an optical amplifier 1804, withan attenuator 2716, and into the second port 2702. A left path 2714 goesthrough a first left junction 2708, through a second left junction 2722,through a phase shifter 2528, through the middle junction 2728, throughthe optical amplifier 1804, with an attenuator 2716 and into the secondport 2702.

The total delays (phase shifts) in the right path 2712 are preferablysuch that a right beam 2740 following the right path 2712 constructivelyinterferes with a portion of a laser beam 2744 that is transmittedthrough the gate 1806 and out through the port 2704. This portion 2704is injected back into the right path 2712 producing a self-enhancementeffect. To constructively interfere with the transmitted portion of thelaser beam 2744, and thereby reinforce the right beam 2740, the rightbeam phase may be adjusted to a proper phase by a phase shifter 2529 toprovide for proper phase alignment. The gate 1806 is preferably suchthat when the right beam 2740 constructively interferes with thetransmitted portion to the laser beam 2744, it destructively interfereswith the reflected portion of the laser beam 2744 which passes throughthe port 2732 and into the left path 2714. Thus, light returning to thegate 1806 through the right path 2712 through port 2702 reinforces theproportion of the laser beam 2744 transmitted through the gate 1806 andinto the right path 2712 and diminishes the proportion of the laser beam2744 reflected into the left path 2714. As a result, the stronger theright beam 2740, the more the left beam 2742 is starved and the more theright beam 2740 is fed.

The configuration of the left path may be such as to provide ananalogous function of making the left beam 2742 self-reinforcing aswell. That is, the total delays in the left path 2714 are preferablysuch that the left beam 2742 constructively interferes with the portionof a laser beam 2744 that is reflected through the gate 1806 and out theport 2732. To constructively interfere with the reflected portion of thelaser beam 2744, the left beam phase may be adjusted to the proper phaseby phase shifter 2528. When the left beam 2742 constructively interfereswith the reflected portion of the laser beam 2744 exiting through port2732, it destructively interferes with the transmitted portion passingthrough the port 2704 and into the right path 2712. Thus, lightreturning through left path 2714 and through port 2702 reinforces theproportion of the laser beam 2744 reflected into the left path 2714 anddiminishes the portion transmitted into the right path 2712. As aresult, the stronger the left beam 2742, the more the right beam 2740 isstarved and the more the left beam 2742 is fed.

In order to provide the phase relationships required to make each of theleft and right beams 2742 and 2740 self-reinforcing as described, whenthe two beams 2742 and 2740 are merged by junction 2728, theydestructively interfere with each other. As a result of the destructiveinterference, the only light remaining entering the gate 1806 throughport 2702 is a residual resulting from a subtraction of a dominant beam,i.e., the stronger of left and right beams 2742 and 2740, from thesubordinate one of the two beams 2742 and 2740.

If the dominant beam is right beam 2740, the residual entering port 2702will be of such phase as to cause constructive interference with theportion of the laser beam 2744 transmitted in the gate 1806 and causedestructive interference with the portion reflected in the gate 1806.The analogous effect occurs with respect to the left beam 2742. If thedominant beam is left beam 2742, the residual entering port 2702 will beof such phase as to cause constructive interference with the portion ofthe laser beam 2744 reflected in the gate 1806 and cause destructiveinterference with the portion transmitted in the gate 1806. Thecombination of optical amplifier 1804 and attenuator 2716 preferably hasa nonlinear transfer function characterized by a gain curve with alinear gain region and a relatively flat saturation region, such asembodiments discussed with reference to FIGS. 12A to 12K. The transferfunction preferably also provides a net amplification that overcomes allsources of attenuation in the left and right paths (2714 and 2712) suchthat the net gain at the saturation region is at least one. When theoptical amplifier 1804 and attenuator 2716 combination provides thistransfer function, the dominant one of left and right beams 2742 and2740 will increase until the optical amplifier 1804 saturates. At thispoint, the intensity of the residual applied at the port 2702 willpreferable be substantially equal to the intensity of the laser beam2744 applied at port 2706. When these conditions exist, it should beclear from the foregoing that all of the laser beam 2744 will bedirected into the path 2712 or 2714 of the dominant beam 2740 or 2742and substantially none of the laser beam 2744 will be directed into thepath of the 2714 or 2712 of the subordinate beam 2742 or 2740.

The optical amplifier 1804/attenuator 2716 combination preferably have again and saturation plateau (e.g., as indicated at 561A and 516A anddescribed with respect to FIG. 12B) that ensures the self-reinforcementprocess progresses toward a “clamped” stable state without continuing toarbitrarily-high dominant-beam magnitudes. In the absence of inherentbias in the system, if one of the beams 2740 and 2742 becomes dominant,for example due to noise or other perturbation, the process of positivefeedback will iterate continuously with the residual of the dominantbeam reinforcing the dominant beam after the completion of a cycle alongthe dominant beam's path 2714 or 2712. To assure enhanced return of theresidual of the beam that arrives from path 2714, the totalamplification (including the amplification of amplifier 1804, theattenuation loss at the junctions and the attenuator 2716, thepropagation and scattering loss and other losses) along paths 2714 and2712 may be made to be greater than 1. Accordingly after each cyclealong the paths 2712 and 2714 the intensity at port 2702 of the residualof the beam will increase. This process continues until the amplifier1804 saturates, thereby stopping the continuous increase of the dominantbeam and clamping to provide a fixed intensity at port 2702. As stated,preferably, the intensity of the clamped residual beam arriving at 2702is comparable in magnitude to that of the laser beam 2744 when theamplifier 1804 and attenuator 2716 reach the saturation plateau. Byadjusting the attenuation or amplification, the combination of amplifier1804 and attenuator 2716 allows the magnitude of the saturation plateauto be adjusted. The amplifier 1804 ensures the feedback signal is strongenough to overcome losses, while limited amplification to a maximumlevel of the saturation plateau.

To summarize, the dominant beam is diminished by the subordinate beam in2728, which subtracts one beam from the other. Diminution of thesubordinate beam increases the residual passed into 2702 by the junction2728 because of the enhanced difference between the dominant andsubordinate beams. Thus, the dominant beam enhances itself anddiminishes the subordinate beam. Due to inherent loss in junctions 2710,2708, 2722, 2720, and 2728 and also in attenuator 2716, the gain ofamplifier 1804/attenuator 2716 combination should be adjusted to a valuethat ensures bistable operation. The residual, which is applied at 2702enhances the dominant beam and diminishes the subordinate beam byincreasing the flow of laser energy through the gate 1806 and into thepath (2712 or 2714) of the dominant beam.

Once a light path 2714 is clamped to a high level, gate 1806 directsmost of the energy toward path 2714 and very little or none of theenergy is directed by gate 1806 into path 2712. This state in which theintensity at output 2718 is high and the intensity at output 2730 islow, or nulled, is stable and may be identified as L-high. A similarprocess starting with a dominant beam arriving from 2712 will result ina stable state that may be identified as R-high. In the R-high state,the intensity at output 2730 goes high and the intensity at output 2718goes low and ends up substantially nulled. The paths 2714 and 2712 maybe configured such that their propagation delays are only slightlydifferent. For example, such that their phases are π radians differentat port 2702, such that they reinforce or reduce the intensity of therespective light from the laser 1802 reflected or transmitted by thegate 1806, as described above.

From the above description, it should be clear that if the total netgain in the optical loops along paths 2714 and 2712 that start and endat 2702 is greater than 1, and there is no substantial bias favoring theinitial fraction of the energy from the laser 1802 that is transmittedthrough the left 2714 or right 2712 path, the bistable device 1810 willbe unstable. If the energy in both paths 2714 and 2712 is equal, theintensity at port 2702 will be nulled and the self-reinforcement processwill stop, but the equilibrium is unstable. Since each path 2714 and2712 is self-reinforcing, if equal shares of energy are directed alongthe left 2714 and right 2712 paths, the slightest perturbation cause itto shift to one of the two stable states R-high or L-high.

Some of the energy may be tapped from each of the left and right paths2714 and 2712, by way of junctions 2708 and 2710, respectively, intorespective outputs 2718 and 2730. Use of these tapped signals mayinclude driving upstream optical circuits. Using the outputs 2718 and2730, it may be determined which is the current state of the bistabledevice either by comparing the two outputs 2718 and 2730 or by detectingthe signal level on one to infer the state of the other. The bistabledevice 1810 is similar to the bistable device 1865 of FIG. 27A in havingone state in which a right path 2712 has a high signal level (R-high)and another in which a left path 2714 has a high signal level (L-high).

To change a current state of the bistable device 1810, right input 2726and left input 2724 are used. A signal applied at a certain phase angleto the input 2726 may suppress the light traveling through the rightpath 2712 by interference. The input signal may be strong enough toswitch the phase of the light traveling through the right path 2712. Thesuppressed or reversed beam in path 2712 then propagates through rightpath 2712 and combines with any beam in path 2714 in the middle junction2728. If the input signal applied at 2726 is sufficiently strong, thetotal signal going through the port 2702 will be in the phase of thelight in the left path 2714. This phase will enhance the portion of thelaser 1802 light that is directed to the left path 2714 by constructiveinterference, in the gate 1806, with laser 1802 light causing the lightin the left path 2714 to be reinforced. At the same time, the light fromthe laser 1802 directed by the gate 1806 into the right path 2712 willbe diminished by the same interference effect in gate 1806.

Alternatively, instead of suppressing the dominant beam in the rightpath 2712, a subordinate beam in the left path 2714 can be enhanced byapplying a signal of appropriate phase to the left input 2724. This hasthe same effect, on the combined signal inserted through the port 2702,as suppression of the signal in the right path 2712. This is because allthe signals (those in the left 2714, right 2712, and the input signalapplied at either input 2726 or 2724) are added coherently and linearlyto the beam ultimately inserted through port 2702. The phase of anenhancement signal applied at input 2724 is identical to the phase of asuppression signal applied at input 2726 and both arrive at the samedestination.

Thus, a signal entering right input 2726 or one entering left input 2724may be used to shift the state of the bistable device 1810 to L-high.Once the signal is placed in this state, it remains in a stable state.It should be clear that a signal entering left input 2724 or right input2726 may be used to shift the state of the bistable device 1810 fromL-high to R-high by suppressing the signal in the left path 2714 orenhancing the signal in the right path 2712.

The amplifier 1804 may include a nonlinear device to limit the intensityof the signal arriving at port 2702. This may amplify the differencebetween the R-high state and the L-high state. Preferably, in the stablestate, the signal at optical path 2702 matches the laser 1802 signalintensity so that all of the laser light will be directed along one pathor the other 2714 or 2712. In that case, the difference between theR-high and L-high states will be as high as possible. If the signal atpath 2702 is too high, residual signal will remain (in opposite phase)in the subordinate path 2712 or 2714. Such a residual signal may beundesirable for detection or the driving of some upstream processes withthe subordinate output signals 2718 or 2730. The input signal intensityshould be such that the signal at 2702 is of a phase that reinforces thesignal on the right path 2712 or left path 2714, whichever is desired tobe dominant. The input signal must be intense enough to ensure thisphase whether the device starts in L-high state or R-high state. Forexample, when the input signal is applied to switch the state to R-highwhile the device 1810 is in state L-high, the input should be intenseenough that the residual of the dominant left path 2714 signal isdominated leaving a residual at 2702 in the phase of the right path 2712signal.

It is not essential that the net amplification into 2702 have anyparticular value. Higher gain will result in a faster clamping process.This applies to all the bistable embodiments described above and below.If the intensity resulting from the saturated gain is higher than neededto null the energy at one of the paths 2714 or 2712, the residual energyis injected into the path that is currently at the low state (the onethat is preferably nulled) with a reverse phase so that when it combinesat 2728 with the dominant beam in high state, this residual energyconstructively interferes with the dominant beam. As a result, this onlyaccelerates the clamping, but the intensity of the subordinate beamwould be different from zero. This may make detection and discriminationof states more difficult.

Similarly, if the intensity of the saturated gain is lower than neededto null the energy at one of the paths 2714 or 2712, the intensity atthe subordinate beam would be different from zero as well.

It should be clear that high gain accelerates the transition of device1810 from one state to another, since the higher the gain the feweriterations that are needed to clamp the amplifier. It should also berecognized that the saturation level of the combination of amplifier1804 and attenuator 2716 determines how close to zero the intensity ofthe output at the lower state will be.

The amplification in the optical loops that contain paths 2714 and 2712and which start and end at port 2702 is related to the linear slope ofthe gain curve of the transmission function of the combination ofamplifier 1804 and attenuator 2716. The saturation region of thiscombination is independent of the linear slope of the gain. Accordingly,the gain and the saturation level can be adjusted independently and mayhave at the same time high gain and a correct saturation level toprovide rapid convergence to one of the stable states and has, at itsoutputs, an intensity very close to zero when that output is derivedfrom the subordinate beam.

Note that phase shifters 2528 and 2529 may be needed to ensure thephases of the feedback signals carried in left and right paths 2714 and2712 have the proper phase alignment to perform the functions described.That is, they are used to ensure that the signals in the left and rightpaths 2714 and 2712 satisfy the following conditions:

1. They are opposite in phase when combined to form a feedback signal,e.g., the signal applied to the gate 1806 at port 2702.

2. They are applied at the gate 1806 such that the left side 2714 signalreinforces itself by constructively interfering with reflected lightfrom the laser to direct it into path 2714. If the above conditions aresatisfied, the right path 2712 signal will direct laser light into theright path 2712 by the same process.

Phase shifters may be used in other parts of the configuration of FIG.27B as well.

Referring now also to FIG. 27C, the basic configuration of FIG. 27B maybe modified in various ways. For example, the functions of junctions2708 and 2722 (FIG. 27B) may be performed by a single beam splitter2518. Equivalently, the analogous functions of junctions 2720 and 2710(FIG. 27B) may also be performed by the single beam splitter 2518. Thus,each configuration indicated by outlined box 2501 (or 2502) of FIG. 27Bmay be replaced by a configuration 2503 as shown in FIG. 27C. Forexample, an input beam 2510 may serve as FIG. 27B input 2724 and anoutput 2514 may serve as it's output 2718. The path 2714 of FIG. 27Bcorresponds to the beam 2512 reflected into beam 2516. Similarly, usingthe same type of beam splitter 2518, the configuration indicated byoutlined box 2502 may be replaced with the configuration of 2503.

Referring now also to FIG. 27E, the embodiment of FIG. 27B may alsomodified to replace the beam splitter gate 1806 with one based on adirectional coupler 2525. The input and output ports 2706 and 2702 and2704 and 2732 perform substantially the same functions as the beamsplitter 1806, as long as each is configured properly as will beunderstood by those of skill in the relevant art. Thus, a laser appliedat 2706 will direct its energy into a bar beam output at 2704 and across beam output at 2732. As should be evident to those of skill in theart, the directional coupler 2525 may be configured such that properlyphase-aligned return paths will provide the same behavior in directionalcoupler 2525 as described with respect to beam splitter 1806 in theconfiguration of FIG. 27B as long as proper phase shifts will be used.

Referring to FIG. 27B, although the paths 2714 and 2712 and others areillustrated in FIG. 27B in a manner that is suggestive of waveguides, itis clear that mirrors 2529A of FIG. 27D could be used to guide the beamson left and right paths 2714 and 2712 as well as others. A beam splitter(not shown) may be used in place of junction 2728 to join the two beamson paths 2712 and 2714 guided by mirrors, such as mirror 2529A of FIG.27D, into the port 2702. In such a configuration, the functions ofjunctions 2720, 2710, 2722, and 2708 may be performed by beam splitters(not shown) as well. Note also that the illustrations of the paths 2712and 2714, which are suggestive of waveguides, are schematic only and ina real structure may be curved gradually to minimize attenuation.

Referring to FIG. 28A, another embodiment of a bistable device 2101employs a laser source 2116 to inject a continuous beam 2113 through anisolator 2114 into a port 2112 of a beam splitter 2110, for example adielectric beam splitter. The isolator 2114 prevents light returningfrom the same port 2112 from entering the laser source 2116. Light fromthe laser is applied to the beam splitter 2110 and divided thereby intoa transmitted beam 2121A (going clockwise around the path 2119) and areflected beam 2121B (going counterclockwise around the path 2119),which flow in opposite directions along the same path 2119. Thetransmitted beam 2121A is transmitted by the beam splitter 2110 andtherefore suffers no phase change compared to the reflected beam 2121B,which suffers a π/2 radian phase change after being reflected by thebeam splitter 2110. The transmitted and reflected beams 2121A and 2121Bare guided around the path 2119 by reflectors 2124 and 2130 back to thebeam splitter 2110.

At the beam splitter, part of the transmitted beam 2121A is transmittedagain by the beam splitter 2110 into a path 2107 and part of thereflected beam 2121B is reflected again by the beam splitter 2110 intothe same path 2107. The now twice-reflected beam 2121B and the twicetransmitted beam 2121A are simultaneously inserted via the beam splitter2110 into the same path 2107. The beams 2121A and 2121B propagate towarda reflector 2104 and back along the same path 2107 to the beam splitter2110. Since the reflected beam 2121A is reflected twice, it suffers twophase rotations of π/2 radians compared to the transmitted beam 2121Awhose phase is not rotated at all. Because of the opposite phases of thetwo beams 2121A and 2121B, when they propagate along path 2107, theycancel each other along this path, causing all of the light to propagatetoward the isolator 2114 where it is blocked from entering back into thelaser 2116. This is because on the path 2107, the reflected beam 2121Bis π radians out of phase with the transmitted beam 2121A, and on thepath out the port 2112, they are in phase.

As the two beams 2121A and 2121B propagate along path 2107, they areamplified by an optical amplifier 2108 and an attenuator 2106cooperating to produce a nonlinear gain curve similar to that discussedwith regard to FIG. 12B, above. The two beams 2121A and 2121B passthrough a phase shifter 2100 which adjusts the phase angles at which thetwo beams 2121A and 2121B interfere with the beam 2113 from the laser2116 within the beam splitter 2110. Both the transmitted and reflectedbeams 2121 A and 2121B are adjusted by the same amount, since theirpaths 2107 are identical.

Initially, since the two beams 2121A and 2121B cancel each other alongthe path 2107, when they return to the beam splitter 2110, they have noeffect on the beam 2113 from the laser 2116. However, if someperturbation (or inherent bias) causes one of the two beams 2121A or2121B to be slightly stronger than the other, the dominant beam will notbe completely canceled by the subordinate beam and a residual of thedominant beam will be applied at the port 2111 of the beam splitter2110. The phase shifter 2100 may be adjusted such that the dominant beamreinforces itself by directing a larger fraction of the laser beam 2113to be transmitted along in its direction along the path 2119. Forexample, if the dominant beam is the transmitted beam 2121A, theresidual applied at 2111, assuming the phase adjustment is correct, willinterfere constructively with the portion of the laser beam 2113 that istransmitted by the beam splitter 2110 and thereby added to thetransmitted beam 2121A. Similarly, if the dominant beam is the reflectedbeam 2121B, the residual applied at 2111, assuming the phase adjustmentis correct, will interfere constructively with the portion of the laserbeam 2113 that is reflected by the beam splitter 2110 and thereby addedto the reflected beam 2121B.

The path 2119 contains multiple beam splitters 2120, 2122, 2138, and2136, which cause significant attenuation of the beams 2121A and 2121B.In addition, reflectors 2124, 2130, and 2104, the beam splitter 2110,the phase shifter 2100, and the free paths 2119 and 2107 may beresponsible for attenuation as well. As a result, the residual may berelatively weak compared to the laser beam 2113 and have little biasingimpact on it, unless compensated by the optical amplifier 2108. Toovercome the net attenuation of the various paths, the amplifier2108/attenuator 2106 combination may be configured such as to causesufficient gain to overcome these losses such that the residual of thedominant one of beams 2121A and 2121B will progressively increase itselfthrough the feedback mechanism of constructively interfering with theportion of the laser beam 2113 that feeds the dominant beam anddestructively interfering with the portion that feeds the subordinatebeam. The amplifier 2108/attenuator 2106 combination is preferablyconfigured to provide a maximum output (i.e., when the optical amplifier2108 is saturated) that substantially matches that of the laser beam2113. Thus, when the dominant beam progresses toward the maximum definedby saturation of the amplifier 2108, it will cause the entire beam 2113to be fed into the dominant beam path by constructive interference inthe beam splitter 2110. Correspondingly, all of the subordinate beamwill be nulled by destructive interference by the same dominant beamresidual.

First and second outputs 2126 and 2134 are obtained by tapping some ofthe energy from the two beams 2121A and 2121B by means of the respectivebeam splitters 2122 and 2136, respectively. Some of the light in thetransmitted beam 2121A is tapped by the beam splitter 2122 to form afirst output 2126 and some of the light in the reflected beam 2121B istapped by the beam splitter 2136 to form a second output 2134. The firstand second outputs 2126 and 2134 may be used to determine which of thetransmitted and reflected beams 2121A and 2121B is dominant, thereby toindicate a current state of the bistable device 2101. To change thestate of the bistable device 2101, input signals 2140 and 2142 may beadded in a phase alignment such that they interfere with the transmittedand reflected beams 2121A and 2121B, respectively. That is, input 2140may be used to inhibit transmitted beam 2121A, by destructiveinterference in beam splitter 2120 and input 2142 may be used to inhibitreflected beam 2121B, by destructive interference in beam splitter 2138.Alternatively, input 2140 may be used to enhance transmitted beam 2121A,by constructive interference in beam splitter 2120 and input 2142 may beused to enhance reflected beam 2121B, by constructive interference inbeam splitter 2138.

By reducing transmitted beam 2121A, using the input 2140, the state ofthe bistable device 2101 may be changed from a state where thetransmitted beam 2121A is high to a state where the reflected beam 2121Bcan become the dominant beam and thereby progress toward a stable statein which the reflected beam 2121B receives all the laser beam energy2113 by interference in beam splitter 2110. By enhancing transmittedbeam 2121A, using the input 2140, the state of the bistable device 2101may be changed from a state where the reflected beam 2121B is high to astate where the transmitted beam 2121A can become the dominant beam andthereby progress toward a stable state in which the transmitted beam2121A receives all the laser beam energy 2113 by interference in beamsplitter 2110. Analogous effects can be achieved by enhancing orsuppressing the reflected beam 2121B by means of a suitable input 2142applied to beam splitter 2138. In both instances, enhancing one of thebeams 2121A or 2121B requires a phase of the corresponding input signal2140 or 2142 to be opposite the phase used to suppress the one of thebeams 2121A or 2121B.

Note that because some of the energy in the reflected beam 2121B istransmitted back toward the laser 2116 by the beam splitter 2110 andsome of the energy in the transmitted beam 2121A is reflected backtoward the laser 2116 by the beam splitter 2110, the isolator 2114prevents this light from entering the laser cavity.

It should be clear from the above description that the device of FIG.28A has two stable states which start with an initial unstableequilibrium generated by the device. It should also be clear that thereis a substantial analogy between device 1810 of FIG. 27B and the device2101 of FIG. 28A in terms of how they operate and the bistable behaviorachieved. In both, a process begins with an unstable state in which allthe light is directed by an interference device (e.g., 2110) away from afeedback path (e.g., 2107) and no light is directed along the feedbackpath (e.g., 2107) due to destructive interference between the portionsof the beams that arrive back at the interference device (e.g. 2110). Atransition to a certain stable state starts due to some perturbationthat makes one of the beams (e.g. 2121A or 2121B) dominant or it isinherent due to bias in the system. The residual of the dominant beamreturns to the interference device 2110 and enhances the intensity ofthe light following its own path while diminishing the intensity of thelight in the subordinate path. This process continues as the residual ofthe dominant beam is reinforced by one or more iterations through thecircuit. The process continues till the intensity at the feedback pathis clamped to a saturation level by means of a nonlinear amplificationdevice.

To assure on going transition to a stable state, the net gain along thefeedback path (e.g., 2107 or 2119) should be greater than 1. To assurethat the intensity of the subordinate beam, tapped by the outputs (e.g.,2126 or 2134), is close to zero, the clamped intensity of the residualbeam on the feedback path (e.g., 2107) should be similar to theintensity of the beam from the laser arriving at the interference device(e.g., 2110).

To flip the stable state of the device (that is, to reverse it to itsother stable state), an input signal is inserted at an input thatsuppresses the dominant beam or enhances the subordinate beam. Theintensity at the input should be strong enough to inhibit the lightintensity of the dominant beam so the residual beam at the feedback path2107 will be dominated by the previously subordinate (and now-dominant)beam, thereby reversing the subordinate and dominant beams.

As mentioned, instead of suppressing the dominant beam using an inputsignal, the bistable can be switched by choosing the phase of arespective input signal to enhance the subordinate beam. In this case,the intensity of the input beam should be strong enough to increase thelight intensity of the subordinate beam such that the subordinate beamovercomes the dominant beam. Once that is true, the once-subordinatebeam residual will enhance itself and suppress the once-dominant beam byfeedback. As soon as the process starts, it flywheels until the newstable state is reached. The switch from one beam dominating to theother in the residual beam along common path 2107 results in theswitching between the stable states of the device.

Referring to FIG. 28B, another embodiment of a bistable device made ofplanar waveguides or fiber optics employs a laser source 2216 to injecta continuous beam 2213 through an isolator 2214 along a path 2212 into adirectional coupler 2210. An isolator 2214 prevents light returning fromthe same port 2212 from entering back into the laser source 2216. Lightfrom the laser is applied to the directional coupler 2210 and dividedthereby into a bar beam 2221A (going counter-clockwise around the path2219) and a cross beam 2221B (going clockwise around the path 2219),which flow in opposite directions along the identical path 2219. The barbeam 2221A is transmitted by the directional coupler 2210 and thereforesuffers no phase change compared to the cross beam 2221B, which suffersa π/2 radian phase change after crossing over the directional coupler2210. The bar and cross beams 2221A and 2221B are guided around the path2219 which may be implemented as a waveguide, back to the directionalcoupler 2210.

At the directional coupler 2210, part of the bar beam 2221 A passesagain in a bar direction through the directional coupler 2210 into path2207 and part of the cross beam 2221B again crosses over the directionalcoupler 2210 into round trip path 2207 terminated by a reflecting loop2204. The cross beam 2221B crosses over the directional coupler 2210twice and the bar beam 2221A passes through it twice in a bar direction.Both are simultaneously inserted via the directional coupler 2210 intothe same path 2207 which progresses toward loop 2204 and back along thesame path 2207 to the directional coupler 2210. Since the cross beam2221B crosses the directional coupler 2210 again, it suffers anotherphase rotation of π/2 radians compared to the bar beam 2221A whose phaseis not rotated at all. When the bar and cross beams 2221A and 2221B aremerged on path 2207, they cancel each other along this path, causing allof the light to propagate toward the isolator 2214 where it is blockedfrom entering the laser 2216. This is because on the path 2207, thecross beam 2221B is or radians out of phase related to the bar beam2221A, and on the path out the port 2212, they are in phase.

As the two beams 2221A and 2221B propagate along path 2207, they areamplified by an optical amplifier 2208 and an attenuator 2206cooperating to produce a nonlinear gain curve similar to that discussedwith regard to FIG. 12B, above. The two beams 2221A and 2221B passthrough a phase shifter 2200 which adjusts the phase angles at which thebar and cross beams 2221A and 2221B interfere with the beam 2213 fromthe laser 2216 within the directional coupler 2210. Both the bar andcross beams 2221A and 2221B are adjusted by the same amount, since theirpaths 2207 are identical.

Initially, since the two beams 2221A and 2221B cancel each other alongthe path 2207, when they return to the directional coupler 2210, theyhave no effect on the laser beam 2213 from the laser 2216. However, ifsome perturbation (or inherent bias) causes one of the two beams 2221Aor 2221B to be slightly stronger than the other, the dominant beam willnot be completely canceled by the subordinate beam and a residual of thedominant beam will be applied at the port 2211 of directional coupler2210. Phase shifter 2200 may be adjusted such that the dominant beamreinforces itself by directing a larger fraction of the laser beam 2213to be transmitted along in its direction along the path 2219. Inaddition, the subordinate beam is further diminished by theself-reinforcement of the dominant beam because the interference thatreinforces the dominant beam also inhibits the subordinate beam. Forexample, if the dominant beam is the bar beam 2221A, the residualapplied at 2211, assuming the phase adjustment is correct, willinterfere constructively with the portion of the laser beam 2213 that issent in the bar direction by the directional coupler 2210 and therebyadded to the bar beam 2221A. It will concomitantly suppress the portionof the laser beam 2213 that is sent in the cross direction by thedirectional coupler 2210 and thereby reduce the cross beam 2221B. Theconstructive interference with the portion of the laser beam 2213 thatgoes in the bar direction over the directional coupler 2210 also resultsin a diminution of the portion that crosses over into the bar beam 2221B. Similarly, if the dominant beam is the cross beam 2221B, theresidual applied at 2211, assuming the phase adjustment is correct, willinterfere constructively with the portion of the laser beam 2213 that iscrossed over by the directional coupler 2210 and thereby added to thecross beam 2221B. The constructive interference with the portion of thelaser beam 2213 that goes in the cross direction over the directionalcoupler 2210 also results in a diminution of the portion that goes inthe bar direction into the bar beam 2221B.

The path 2219 contains multiple optical couplers 2220, 2222, 2238, and2236, which cause significant attenuation of the beams 2221A and 2221B.In addition, the directional coupler 2210 and the phase shifter 2200,etc. may be responsible for attenuation as well. As a result, theresidual may be relatively weak compared to the laser beam 2213 and havelittle biasing impact on it, in the absence of amplification tocompensate. To overcome the attenuation of the various paths, theamplifier 2208/attenuator 2206 combination may be configured such as tocause sufficient gain to overcome these losses such that the residual ofthe dominant one of beams 2221A and 2221B will progressively increasesitself through the feedback mechanism. The feedback mechanism includesthe residual constructively interfering with the portion of the laserbeam 2213 that feeds the dominant beam and destructively interferingwith the portion of the laser beam 2213 that feeds the subordinate beam.The amplifier 2208/attenuator 2206 combination is preferably configuredto provide a maximum output that coincides with a saturation conditionof the optical amplifier 2208/attenuator 2206 combination also referredin the instant specification as “clamped” intensity that substantiallymatches that of the laser beam 2213. Thus, when the dominant beamprogresses toward its maximum, it will cause the entire beam 2213 to befed into itself by constructive interference in the directional coupler2210. At the same time, the portion of the laser beam 2213 that goesinto the subordinate beam is nulled.

First and second outputs 2226 and 2234 are obtained by tapping some ofthe energy from the two beams 2221A and 2221B by means of the respectiveoptical couplers 2222 and 2236. Some of the light in the bar beam 2221Ais tapped by the optical coupler 2222 to form a first output 2226 andsome of the light in the cross beam 222 1B is tapped by the opticalcoupler 2236 to form a second output 2234. The first and second outputs2226 and 2234 may be used to determine which of the bar and cross beams2221A and 2221B is dominant, thereby to detect a current state of thebistable device 2201.

To change the state of the bistable device 2201, input signals 2240 and2242 may be added in a phase alignment such that they destructivelyinterfere with the bar and cross beams 2221A and 2221B, respectively.That is, input 2240 may be used to inhibit bar beam 2221A, bydestructive interference in optical coupler 2220 and input 2242 may beused to inhibit cross beam 2221B, by destructive interference in opticalcoupler 2238. Alternatively, the state of the bistable device 2201 maybe changed by input signals 2240 and 2242 by adding in a phase alignmentsuch that they constructively interfere with the bar and cross beams2221A and 2221B, respectively. That is, input 2240 may be used toenhance the bar beam 2221A and input 2242 may be used to enhance thecross beam 2221B. By reducing bar beam 2221A using the input 2240, thestate of the bistable device 2201 may be changed from a state where thebar beam 2221A is high to a state where the cross beam 2221B can becomethe dominant beam and progress toward a stable state in which the crossbeam 2221B receives all the laser beam 2213 energy by interference indirectional coupler 2210. In this state, the bar beam 2221A receivessubstantially none of the laser beam 2213 energy. By increasing the barbeam 2221A using the input 2240 in an opposite phase, the state of thebistable device 2201 may be changed from a state where the cross beam2221B is high to a state where the bar beam 2221A can become thedominant beam and progress toward a stable state in which the bar beam2221A receives all the laser beam energy 2213. In this state, the crossbeam 2221B receives substantially none of the laser beam 2213 energy. Inanalogous manner, the cross beam 2221B may be enhanced to switch from astate where the bar beam 2221A is dominant or diminished to switch thebistable device 2101 from a state where the cross beam 2221B isdominant.

Note that because some of the energy in the bar and cross beams 2221Aand 2221B is transmitted back toward the laser 2216 by the directionalcoupler 2210 and Some of the energy in the bar beam 2221A is reflectedback toward the laser 2216 by the directional coupler 2210, the isolator2214 prevents this light from entering the laser cavity.

It should be clear from the above description that the device of FIG.28B has two stable states that start with an initial unstableequilibrium existing at the initial state of the device 2201. It shouldalso be clear that there is substantial analogy between devices 1810 ofFIG. 27B, 2101 of FIG. 28A, and the device 2201 of FIG. 28B in terms ofhow they operate and the bistable behavior achieved. In both, a processbegins with an unstable state in which all the light is directed by aninterference device (e.g., 2210) away from a feedback path (e.g., 2207)and no light is directed along the feedback path (e.g., 2207) due todestructive interference between the portions of the beams that arriveback at the interference device (e.g. 2210). A transition to a certainstable state starts due to some perturbation that makes one of the beams(e.g. 2221A or 2221B) dominant or it is inherent due to bias in thesystem. The residual of the dominant beam returns to the interferencedevice and enhances the intensity of the light following its own pathwhile diminishing the intensity of the light in the subordinate path.This process continues as the residual of the dominant beam isreinforced by each iteration through the circuit. The process continuestill the intensity at the feedback path is clamped to a saturation levelby means of a nonlinear amplification device. To assure on goingtransition to a stable state, the net gain along the feedback path(e.g., 2207 or 2219) should be greater than 1. To assure that theintensity of the subordinate beam, tapped by the outputs (e.g., 2226 or2234) is close to zero, the clamped intensity of the residual beam onthe feedback path (e.g., 2207) should be similar to the intensity of thebeam from the laser (e.g. 2216) arriving at the interference device(e.g., 2210).

To flip the stable state of the device and thereby reverse it to anopposing stable state, an input signal is inserted at an input thatsuppresses the dominant beam or enhances the subordinate beam. Theintensity at the input should be strong enough to reverse the differencebetween the current dominant and subordinate beams such that theresidual's phase switches to that of the subordinate component. This canbe done by enhancing the subordinate beam or suppressing the dominantbeam.

Referring now to FIG. 28D, a bistable embodiment that is similar to thatof FIG. 28A directs transmitted and reflected beams 2321A and 2321B froma beam splitter 2310 along separate transmitted and reflected paths2319A and 2319B. Recall that in the embodiment of FIG. 28A, thetransmitted and reflected beams 2121A and 2121B went in oppositedirections along an identical path 2119 (FIG. 28A). Both beams 2321A and2321B return to the beam splitter 2310 after being reflected byrespective reflectors 2330 and 2324 and are directed into a common path2307 by beam splitter 2310. To arrive at common path 2307, reflectedbeam 2321B is transmitted through the beam splitter 2310 and transmittedbeam 2321A is reflected by the beam splitter 2310. That is, thetransmitted beam 2321A returns to the beam splitter 2310 backwardlyalong the path 2319A and is reflected into the path 2307. Similarly,since the reflected beam 2321B returns to the beam splitter 2310backwardly along the path 2319B, it is transmitted into the path 2307.

Each beam 2321A and 2321B suffers one reflection and one transmissionthrough the beam splitter 2310. This is in contract to the situation inthe embodiment of FIG. 28A where the reflected beam 2121B suffered tworeflections and the transmitted beam 2121A suttered two transmissions.Thus, both beams 2321A and 2321B are phase-rotated by π/2 radians by therespective reflections. Another difference in the present embodimentfrom that of FIG. 28A is that since the two paths 2319A and 2319B arecompletely different, one beam, either transmitted beam 2321A orreflected beam 2321B can arrive at common path 2307 with a differentphase from that of the other. A phase shifter 2309 in path 2319A can beused to adjust the relative phases of the transmitted and reflectedbeams 2321A and 2321B when they are inserted into path 2307. If thephase shifter 2309 is adjusted properly, the phase angle between thebeams 2321A and 2321B will be π and the two beams 2321A and 2321B willcancel each other at path 2307. Note that the phase shifter 2309 can belocated on path 2319B to provide the same function. The transmitted andreflected beams 2321A and 2321B return to the beam splitter 2310 and aresubsequently transmitted and reflected by it again and interfere withlaser light 2313 from the laser 2316. Some of the beam energy from beams2321A and 2321B may return to the laser 2316 by passing through port2312, but this energy will be blocked by isolator 2314.

As discussed above, the phase alignments of transmitted and reflectedsignals 2321A and 2321B on path 2307 should be such that:

1. They are opposite in phase when combined to form a feedback signal,e.g., the signal in the feedback path 2307 and inserted back into thebeam splitter 2310 via port 2311.

2. They are applied to the port 2311 on return to the beam splitter 2310such that the transmitted signal 2321A reinforces itself byconstructively interfering with light from the laser light 2313transmitted into path 2319A and destructively interfere with laser light2313 reflected into the path 2319B. If the above conditions aresatisfied, the reflected signal 2321B will direct laser light 2313 intothe reflected path 2319B.

As in the embodiment of FIG. 28A, if one beam 2321A and 2321B becomesdominant, it will reinforce itself in a manner that is analogous to thebehavior of the device of FIG. 28A, which should be clear from the abovediscussion. The optical amplifier 2308 and attenuator 2306 perform thesame functions in the present embodiment and in the embodiment of FIG.28A.

Other parts of the circuit perform analogous functions to theircounterparts in FIG. 28A. That is, the input beam splitters 2338 and2320 and the output beam splitters 2322 and 2336 perform functions thatare essentially the same as performed by the input beam splitters 2138and 2120 and the output beam splitters 2122 and 2136 in the embodimentof FIG. 28A. Input signals 2340 and 2342 interfere with both beams 2321Aand 2321B and thereby may be used to control them to provide forswitching of stable states of the system.

Note that the input beam splitters 2338 and 2320 are located in thecommon path 2307, which corresponds to the common path 2107 of theembodiment of FIG. 28A. This is an alternative location for the inputbeam splitters 2338 and 2320 which may be applied to the embodiment ofFIG. 28A as well, since they have the effect of canceling respectivebeams 2321A or 2321B by virtue of the relative phase of the input beam2342 or 2340 to the transmitted and reflected beams 2321A and 2321B.

Referring also to FIG. 28C, note that in either embodiment 2301 of FIG.28D or 2101 of FIG. 28A, the input beam splitters 2338 and 2320 could bereplaced with a single beam splitter as indicated at 2317 with therespective inputs 2342A and 2340A, applied from opposite sides, toachieve the same effect. Note also, that a single input 2342A and 2340Amay be used with different phases to switch the bistable device (2301 orany of the others). Also note that an attenuator (not shown) might berequired in the path 2319B to balance the effect of the phase shifter2309 so there is no significant bias in the beams 2321A and 2321B.

While the embodiment 2301 has two input beam splitters 2338 and 2320, asingle beam splitter may be used in an alternative configurationindicated generally at 2317 of FIG. 28C. This beam splitter 2343 may belocated on the common path 2307 to combine input signals 2340A or 2342Ato transmitted and reflected beams 2321A and 2321B. In thisconfiguration, input 2342A may be added to beam 2321A and 2321B toenhance or diminish them respectively, depending on its phase, while thebeams are propagating upwardly in the figure and input 2340A may beadded to beams 2321A and 2321B to enhance or diminish them,respectively, while the beams are propagating downward. If the phase ofeither input 2340A or 2342A can be changed selectively, then only oneinput 2340A or 2342A may be required since the effect of adding onephase may be to diminish a first of the beams while enhancing the secondwhile the effect of adding another opposite phase may be to diminish thesecond of the beams while enhancing the first.

All the other components of the embodiment 2301 of FIG. 28D, includingthe phase shifter 2300, reflector 2304, laser 2316, isolator 2314, ports2350 and 2352 and outputs 2326 and 2334 perform functions that areanalogous to the functions of heir counterparts in the embodiment 2101of FIG. 28A as should be clear from the above discussion. Beam splitters2336 and 2322 extract some of the energy from beams 2321A and 2321B intooutput signals 2334 and 2326, respectively, to drive upstream devices(not shown) or indicate a current state of the bistable device 2301.Alternatively, only one output beam splitter 2336 or 2322 may be usedbecause the state of one implies the state of the other.

Referring now to FIG. 28E, an embodiment that is similar to that of FIG.28D, but which uses waveguides and directional coupler devices for beamsteering and summing. As in the 2201 embodiment of FIG. 28B, adirectional coupler 2410 is used to separate bar and cross beams 2421Aand 242 1B. However, unlike the FIG. 28B embodiment, and as inembodiment 2301 of FIG. 28D, the bar and cross beams 2421A and 2421Btake separate paths 2419A and 2419B, respectively, to be reflected byrespective loops 2430 and 2424. These two beams 2421A and 2421B returnto the directional coupler 2410 via respective ports 2452 and 2450. Thebar beam 2421A returns from its loop 2430 then crosses the directionalcoupler 2410 through port 2411 and is inserted into a common path 2407which it loops through a return loop 2404 and back to the port 2411. Thecross beam 2421B returns from its loop 2424 then goes in a bar directionthrough the directional coupler 2410 through port 2411 and is insertedinto the common path 2407 which it loops through a return loop 2404 andback to the port 2411. Thus, both beams 2421A and 2421B are combined incommon path 2107. A phase shifter 2409 performs a function that isessentially the same as the phase shifter 2309 of the embodiment 2301 ofFIG. 28D in that it ensures the phases of the two beams 2421A and 2421Bare opposite. That is, it ensures the bar and cross beams 2421A and2421B are inserted in a common path 2407 such that they are subtracted.When the beams 2421A and 2421B are equal, a null beam is applied to theport 2411 and when they are unequal, a residual of the beams 2421A and2421B is applied at port 2411.

The residual determines the phase applied at port. A phase shifter 2409is adjusted to ensure that the beams 2421A and 2421B return to thedirectional coupler 2410 in such a phase that any residual due toimbalance in the two beams 2421A and 2421B has a self-reinforcing effecton the dominant beam as in the previous embodiments. Specifically, whenthe residual beam results due to the bar beam 2421 A being dominant, thephase of the residual applied at port 2411 will be opposite the phaseapplied a port 2411 when the residual beam results due to the cross beam2421B being dominant. If the cross beam 2421B is dominant, the phase ofthe residual signal applied at 2411 will constructively interfere in thedirectional coupler 2410 with the light from the laser 2416 enteringport 2412 and leaving through port 2450. At the same time, the sameresidual will destructively interfere with light from the laser 2416entering port 2412 and leaving through port 2452. Concomitantly, if thebar beam 2421A is dominant, the phase of the residual signal applied at2411 will constructively interfere in the directional coupler 2410 withthe light from the laser 2416 entering port 2412 and leaving throughport 2452. At the same time, the same residual will destructivelyinterfere with light from the laser 2416 entering port 2412 and leavingthrough port 2450. Thus, the dominant beam will reinforce itself as inother bistable embodiments. Again, as in the other embodiments, anamplifier 2408 and attenuator 2406 provides non-linear amplification toovercome losses in the circuit and ensure state-clamping. Also, lightreturning to the laser from port 2412 is blocked from entering the lasercavity by isolator 2414.

As in the embodiment of FIG. 28B, optical junctions 2438, 2420, 2422,and 2436 are used as link input 2432 and 2440 and output signals 2426and 2434, with various portions of the circuit of 2401, respectively. Aswith other embodiments, it is possible to use only one of the inputs bychanging the phase of the applied signal to enhance the subordinate orsuppress the dominant beam. Also it is possible to use only one of theoutput signals 2426 and 2434 to detect the current state of the device2401. The details of how the bistable 2401 changes state will not bedescribed in further detail here since the roles of the componentsshould be clear from the discussions of FIGS. 28A–28D.

Referring to FIG. 29A, various bistable device embodiments have beendiscussed. In the further embodiments below, various applications ofbistable devices are discussed. For convenience in discussing suchapplications of bistable devices, a reference embodiment of a bistabledevice 1866 will now be described.

As should be clear form the foregoing, the bistable devices, exemplifiedby bistable device 1866, may include one or more inputs. For example,inputs 2835 and 2840, may be provided to introduce biasing signals tochange the state of the bistable device. Each input 2835 and 2840 mayapply signals of a respective phase to form a residual signal 2855 thatis applied to an interference device 2800. Alternatively, a single input(e.g., input 2835) may be used whose phase is changed to effectstate-switching of the bistable device 1866. The residual signal 2855biases the interference device 2800 to direct energy from a power signal2810 to direct its energy in favor of one of multiple state signals2850, which are fed back to the combiner 2805.

The combination of state signals 2850 which the one or more inputs 2835and 2840 as well as an extraction of energy to provide an output 2830 isrepresented by the single combiner 2805. An alternative location isshown for the output 2830 at 2831. The interference device 2800 receivesthe residual signal 2855 and coherently combines it with energy from thepower source 2810 (e.g., a laser) to form the state signals 2850.Although not shown, the signals may be controlled to ensure proper phasealignment and amplified with a nonlinear amplification device.

The illustration of FIG. 29A is an abstraction in which each part maycorrespond to one or more parts of an embodiment. For example, in theembodiment of FIGS. 28C and 28D, the combiner 2805 represents the beamsplitter 2343, which coherently combines two inputs 2340A and 2342A withthe feedback state signal 2850. One or both of the outputs 2334 and 2326correspond to the outputs 2830 or 2831. The transmitted beam 2321A isrepresented by the state signals 2850 and the reflected beam isrepresented by the residual signal passing through the port 2311 intothe beam splitter 2310. The laser 2316 corresponds to the power source2810.

Referring to FIG. 29B, in a toggle application of the bistable device1866, the two inputs 2835 and 2840 are used. The output 2830 may be oneor more outputs, depending on the configuration and the requirements ofan external circuit. A signal splitter 2875 applies a single inputsignal 2865 to the first and second inputs 2835 and 2840. In thisconfiguration, each input signal flips the state of bistable device 1866from its current stable state to its other stable state.

Referring to FIG. 29C, the bistable device 1866 may also be configuredto function as a monostable device. The output is identified as 2830 andmay be one or both outputs indicated in the foregoing or laterembodiments to be discussed. Such a device accepts a single input at2866 and distributes it through a signal splitter 2870 to a delay line2869 on the left input 2835 of the bistable device 1866 and to the rightinput 2840 of the bistable device 1866. Thus, a signal applied to theinput 2866 propagates to the right input 2840 immediately and only aftera delay to the left input 2835. As a result, the bistable device 1866goes into the R-high state initially and then reverts to the L-highstate. To ensure the bistable device 1866 is in the L-high stateinitially, a reset 2868 may be used to place it in such state. The needfor the reset may depend on the application.

Referring to FIG. 29D, the bistable device 1866 may also be configuredas an addressable device. The output is identified as 2830 and may beone or both outputs indicated in the foregoing or later embodiments tobe discussed. The addressable device may pass a signal to one of theleft and right inputs 2835 and 2840 only if it contains a symbolmatching one of the gates 2885 and 2880. Thus, a first symbolcorresponding to gate 2885 switches the bistable device 1866 to theL-high state and a second symbol corresponding to gate 2880 switches thebistable device 1866 to the R-high state. As seen before, such a deviceaccepts a single input at 2867 and distributes it through a signalsplitter 2878 to both branches, passing through a respective symbolmatching gates 2885 and 2880, and leading to both inputs 2835 and 2840of the bistable device 1866.

Referring now to FIG. 30A, an application of the optical monostablediscussed with reference to FIG. 29C, is used to switch a cell 2645. Thecell 2645 is substantially the same as the cell 1621 as described withreference to FIG. 25E in that it contains a header 2647 and payload2634. The header 2647 and payload 2634 are configured to have pulseswith different phase relationships or different (odd vs. even) spacingas described with reference to FIGS. 25C and 25D for the same reasons.Cell (packet) 2645 is divided into two images, image 2623, containingheader 2605 and payload 2610, that is directed through guide 2632 toheader coincidence-gate 2630, and image 2650, containing header 2627 andpayload 2629, that is directed by guide 2613 to coincidence gate 2603.That is, the header 2605 (image of 2647) triggers a coincidence pulse2620 at the output 2642 of header gate 2630 when the delay of the headergate 2630 matches pulse spacing of the header 2605 (2647). As explainedabove, the cell (packet) 2645 is split into two images by a junction2632A, one of which 2623 is applied to the header gate 2630 and theother of which 2650 propagates along a delay path 2613, having a delay2636. If the coincidence pulse 2620 is generated, it triggers theoptical monostable 2600 which generates a long pulse 2625 on a singleoutput 2640.

As should be clear from the foregoing discussion and particularly thediscussion of the monostable shown in FIG. 29C, the output 2640 may beeither of the outputs that taps energy from one of the two feedbackloops of any of the bistable embodiments. For instance, the output 2640may be the output 2134 of the embodiment of FIG. 28A. In that case, theoptical monostable 2600 would be initially in a state in which thetransmitted beam 2121A of FIG. 28A was the dominant beam. The operationof optical monostable device 2600 of FIG. 30A is explained with theassistance of the illustrations of device 2101 and 1866 shown in FIGS.28A and 29C, respectively. A first image of the coincidence pulse 2620on the direct line 2840 (FIG. 29C) would be applied to either the input2140 or 2142 (FIG. 28A) at such phase as either to suppress the dominanttransmitted beam 2121A or enhance the subordinate reflected beam 2121B.If need be, the image of the pulse 2620 may be amplified. This causesthe bistable to switch its state until the second image of thecoincidence pulse 2620 on the delayed line 2835 (FIG. 29C) arrives onthe other input (or same input) either to suppress the dominantreflected beam 2121B or enhance the subordinate transmitted beam 2121A.While the reflected beam 2121B is dominant, the output 2134 has a highsignal and thus, for this interval, a long pulse is generated asindicated at 2625 (FIG. 30A). This pulse 2625 is applied, to coincidencegate 2603, in a manner similar to the pulse 1620D in FIG. 25E to causecell (packet) 2650 to be passed through the coincidence gate 2603 and toappear at output 2621 as call (packet) 2651.

As in the embodiment of FIG. 25B that is used for the purposes of cellsand packets routing, multiple instances of the cell (packet) switch ofFIG. 30A may be tied to a common input 1788 (FIG. 25B), eachcorresponding to the blocks labeled 1551A–1551C and including any numberof cell (packet) switches. The result, as discussed with reference toFIG. 25B, is a demultiplexer capable of switching any size of cells andpackets. It should be clear that in the embodiment of FIG. 30A, theamount of energy that is required in the coincidence pulse 2620 needonly be sufficient to trigger the monostable. As such, the cell (packet)length that can be handled is independent of the energy of this pulse,unlike the embodiment of FIGS. 25A, 25E, and 25K, which must spread theenergy of the coincidence pulse over many pulses of the cells (packets).Note that the delay 2636 is preferably sized to ensure that the cellimage 2650 coincides at the gate 2603 with the long pulse 2625 and inthe proper phase to cause it to produce a coincidence image at theoutput port 2621. Port 2619 of optical monostable 2600 is the reset portof device 2600 and is used, similar to port 2868 of FIG. 29C, todetermine the initial state of device 2600.

Referring to FIG. 30B, in another switch embodiment an optical bistable2656 with respective turn-on and turn-off inputs 2670A and 2670B. Thelatter may correspond to the inputs 2835 and 2840 of the bistabledevices 1866 illustrated in FIGS. 29B–29D and be used to inhibit thedominant beams respective to different states of the bistable device2656. Images of a packet applied at an input 2635 to a distributor 2633are applied to header and tail gates 2630A and 2631, each of whichselects a particular symbol to output a coincidence pulse to therespective on/off the turn-on and turn-off inputs 2670A and 2670B. Animage is also applied to a delay line 2637 which leads to a gate 2603A.Port 2619A of optical bistable 2656 is the reset port of device 2656 andis used, similar to port 2619 of FIG. 30A, to determine the initialstate of device 2656.

Referring also to FIG. 30C, when a header symbol 2666 arrives at theheader gate 2630A of FIG. 30B and matches the gate's delay time, acoincidence pulse is applied to the turn-on input 2670A. When a tailsymbol 2671 arrives at the tail gate 2631 and matches the gate's delaytime, a coincidence pulse is applied to the turn-off input 2670B. Theheader and tail gates 2630A and 2631 may be configured with delaysbetween pulses 2664H and 2662H and 2664T and 2662T, respectively, havingthe same allowed time slots to prevent pulses 2660 (typ.) of payload2668 from triggering a coincidence pulse in either. With appropriatetiming in the delay line 2637, the bistable device 2656 will generate along control pulse which will be applied to the gate 2603A to cause thepayload 2668 to be imaged onto the output 2639 (with or without header2666 and/or tail and 2671) by causing the gate 2603A to form acoincidence signal therefrom.

Note that in the embodiment of FIG. 30B and the method of FIG. 30C, theheader gate 2630A and the tail gate 2631 may be configured to beresponsive only to spaced pulse symbols 2666 and 2671 separated by anodd (or even) number of time slots while the payload pulses 2660(typ.)are located in time slots separating them by an even (or odd-differentfrom the header and tail symbols) number of time slots. Alternatively,the header and tail symbols 2666 and 2671 may employ a different phasedifference between pulse pairs (e.g. 2662H and 2664H or 2662T and2664T), that differs from the phase difference between pulses 2660(typ.) of payload 2668, as in the embodiment of FIG. 25D. Yet anotheralternative is to employ phase only or phase plus pulse-spacing controlor be of a different polarization from the payload pulses 2668. Theabove may benefit from the use of threshold devices. As should be clearwith respect to all of the bistable embodiments above, some minimumlevel of the input signal will be required to cause the bistable toswitch to a target state. This inherent level-discriminating capacitymay be employed to advantage by permitting the use of a symbol scheme inthe address and tail (or address-only for the monstable embodiment),which produces many different output levels. For example, a gate in thesix-phase scheme described with respect to FIG. 23U produces acoincidence pulse only 33% higher, when the phase-symbol matches, thatthe closest missing pulse (where the phase-symbol does not match, but isas close as allowed with matching). It should be clear that the opticalmonostable 2600 (FIG. 30A) or bistable 2656 (FIG. 30B) (or otherbistable embodiments) may be configured such that it does not change itsstate in response to a pulse whose magnitude is 33% lower than themaximal pulse but does change its state when the magnitude of the pulse(e.g. 2620 of FIG. 30A) is at the maximal level. The above appliesequally to other schemes described in the current specification such aspolarization. Thus, the bistable embodiments may be capable ofdiscriminating coincidence pulse levels that are close to the “matching”level, (main coincidence pulses) giving a designer the ability toprovide higher symbol density. Of course the header and tail symbols mayalso employ polarization in a similar manner and may include pulsespacing as well. Thus the bistable and the monostable optical devicesdescribed above may be used also to perform the cancellation of artifactpulses (such as done by the threshold devices described above) by notresponding to pulses having amplitude lower than the amplitude of themain coincidence pulses.

Note that in any of the foregoing embodiments, a reset may be providedto initialize the bistable device to an initial expected state inapplications where an initial state may not be guaranteed. For example,a reset is illustrated at 2868, 2619, 2619A in FIGS. 29C, 30A, and 30B,respectively.

Referring to FIG. 30D, another implementation of a bistable forswitching employs either an optical toggle or optical bistable 2659using a single input 2611. As FIG. 30D is a slight modification of theembodiment describing FIG. 30B, the major of numerical references iskept. In the case of a toggle 2659, the configuration of FIG. 29B,implemented in the design of FIG. 30B, may be used with the single input2611 (FIG. 30D) corresponding to input 2865 (FIG. 29B). Alternatively,the single input 2611 may correspond to an input for any of the bistableembodiments, which applies its signal to either of the beams (thedominant beam or the subordinate beam). Thus, the input device may befor example 2140 or 2142 of FIG. 28A, 2240 or 2242 or FIG. 28B, 2340 or2342 of FIG. 28D, etc.

As discussed with reference to FIG. 29B, when a pulse is received on theinput line 2611 of a toggle, the bistable 2659 may switch from one stateto the other. If the output 2617 is an output indicating the state ofthe subordinate signal of the bistable within the toggle device 2659,then change of state will cause it to indicate the dominant signal andtherefore it will go high. This may happen when a coincidence pulse isgenerated by a header symbol (not shown) as previously discussed withregard to FIGS. 30A and 30B. However, in the present embodiment, thetail symbol (not shown) may be identical to the header symbol. This isbecause a second coincidence pulse from the gate 2630A will switch thetoggle device 2659 again back to the state where the output 2617 goeslow again. It should be clear, in such a case, that if an image of acell (packet) is carried on the delay line 2637, the on-state willproduce a long pulse that coincides with the image of the data cell atthe gate 2603A causing it to be transmitted (with or without the headeror the tail).

In the alternative embodiment where the optical bistable or opticaltoggle 2659 is an optical bistable, the header and tail symbols may beconfigured as shown in FIG. 30E. The relative phases of the pulses areillustrated. A header code, including first pulse 2684H and a secondheader pulse 2682H have a certain phase relationship, both indicated asbeing 3π/2 radians. The payload 2688 pulses, 2680 (typ.), have a phasethat corresponds to the phase that can not produce a main coincidencepulse at header coincidence gate 2630A and thus can not trigger anybistable or toggle device such as device 2659 of FIG. 30D. Pulses 2680(typ.) of payload 2688 are indicated as being at π/2 radians, but thismay be any value different than the header symbol's pulse phases. Thetail symbol 2672 has two pulses 2684T and 2682T whose phases areopposite those of the header symbol 2686.

As should be clear from the discussion of gates, the relative phases oftwo coincidence pulses determines which output of the gate a pulse willemanate from. If both pulses are phase-rotated by an arbitrary amount,it changes the phase of the coincidence pulse by the same amount. Thus,the phase of the coincidence output pulse may be determined by the phaseof the input pulses. In the embodiment of FIG. 30E, the header symbol2686 will produce a coincidence pulse in the address gate 2630A that isopposite in phase to that of the coincidence pulse 2672 produced by thetail symbol. It should be clear that the bistable 2659 may be configuredsuch that if the input is received at one phase, it may enhance thesubordinate beam and if received in the opposite phase, it may diminishthe dominant beam. In either case, it will select a different state.

Referring now also to FIGS. 30F and 30G, thus, the header symbol pulses2674 and 2673, by producing a main coincidence pulse 2681, atcoincidence gate 2630A, of one phase, may place the bistable device 2659in one state and the tail symbol pulses 2678 and 2676, by producing amain coincidence pulse 2682, at coincidence gate 2630A, of oppositephase, may place the bistable device 2659 in the other state. These mayprovide for the bistable device 2659 to turn on in response to theheader symbol 2686 (FIG. 30E) and to turn off in response to the tailsymbol 2672 (FIG. 30E).

While the above description contains many details, these should not beconsidered as limitations on the scope of the invention, but as examplesof the presently preferred embodiments thereof. Many other ramificationsand variations are possible within the teachings to the invention.

For example the all-optical switches, modulators, encoding and decodingsystems, interleaving and multiplexing systems, and demultiplexingsystems have been described for use in communication networks. Howeverthey can be used in other optical systems as well, such as systems usedfor optical backplanes, optical storage networks and optical computing.They also can be used as optical components, devices, and systems inEthernet systems. Although the invention been described using theexamples of Dense Time Division Multiplexing (DTDM) and self-triggeredCDM it can be used for producing very narrow pulses to perform standardtechniques, such as TDM, ATM and packets routing.

Although some systems have been described as modulators they also can beoperated as switches. While some all-optical encoding and multiplexingsystems have been described using sub-units operating as modulators, thesituation can be reversed, i.e., the operation of these same sub-unitscan be change to serve as switches in decoding and demultiplexingsystems. Though some switches and modulators have been described withone output they can include multiple outputs. While the modulators andthe switches have been described as containing gratings or phase arrays,they can also include other interference devices that are capable ofchanging their pitch according to the illumination conditions. Althoughthe gratings and phase arrays have been described as having one orethree interference orders, they are not limited to these numbers ofinterference orders. While some of the switches and the modulators areillustrated without optical amplifiers they can be integrated withoptical amplifiers, such as a Europium Doped Optical Fiber Amplifiers(EDOFA), Solid-state Optical Amplifiers (SOA) or Linear OpticalAmplifiers (LOA).

While some coincidence gates are illustrated when receiving the signalat their inputs from a single source they may receive the signals fromdifferent sources.

While some of the embodiments illustrated in media of open space,radiation guides, fiber optics, waveguides, planar waveguides on a chip,each of them may be produced in any of these media.

Thus the scope of the invention should be determined by the appendedclaims and their legal equivalents, and not by the examples given.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrative embodiments, andthat the present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof.

The present embodiments are therefore to be considered in all respectsas illustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. An all-optical bistable device, comprising: a) a splitting devicehaving first and second inputs and first and second outputs, forreceiving first light beam at said first input and directing said firstbeam as second and third beams propagating through respective first andsecond outputs; b) first optical path between said first output and saidsecond input and second optical path between said second output and saidsecond input for creating combined optical path for said first and saidsecond beams at said second input; c) said combined optical pathincludes a saturable optical amplifier for enhancing and diminishing oneof said second and said third beams for driving said optical amplifierinto a saturation state to create one of two stable states in which oneof said second and said third beams is an enhanced beam and the otherbeam is a diminishing beam; d) at least one tapping device for tappingoutput signal from one of said first and said second optical paths, ande) at least one coupling device for coupling input signal into one ofsaid first and said second optical paths to flip between said two stablestates by converting said enhanced beam into said diminishing beam. 2.The bistable device of claim 1 wherein said splitting device is a beamsplitter.
 3. The bistable device of claim 1 wherein said splittingdevice is a directional coupler.
 4. The bistable device of claim 1wherein said bistable device is made of optical fibers.
 5. The bistabledevice of claim 1 wherein said bistable device is made of optical planarwaveguides.
 6. The bistable device of claim 1 wherein said opticalamplifier is a solid state optical amplifier.
 7. The bistable device ofclaim 1 wherein said at least one of said fist and second optical pathsincludes a phase shifter.
 8. The bistable device of claim 1 wherein saidcombined optical path includes a phase shifter.
 9. The bistable deviceof claim 1 wherein said combined optical path includes an attenuator.10. The bistable device of claim 1 wherein said tapping device selectedfrom a group of beam splitters and directional couplers.